High altitude balloon systems and methods

ABSTRACT

A high altitude lighter-than-air (LTA) system can include a zero-pressure balloon (ZPB) attached in tandem with one or more variable ballast air super-pressure balloons (SPB). The ZPB provides lift for the system while the SPB uses a centrifugal compressor to provide a variable amount of ballast air by pumping in or expelling out ambient air. A solar array coupled with an elongated ladder assembly can be coupled to a payload support for a payload carried by the LTA system. Various advanced performance targets relating to ascent rate, descent rate, range and maximum altitude are achievable with various scaled versions of the basic design of the LTA system. Advanced navigation and control techniques, such as efficient high altitude station-keeping approaches, are made possible with the LTA system.

INCORPORATION BY REFERENCE TO ANY RELATED APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

This application claims the benefit of priority to U.S. provisionalpatent application No. 62/294,189, entitled VARIABLE ALTITUDE AIRBALLAST BALLOON SYSTEM and filed Feb. 11, 2016, to U.S. provisionalpatent application No. 62/294,204, entitled SEMI-AUTONOMOUS TRAJECTORYCONTROL FOR BALLOON FLIGHT and filed Feb. 11, 2016, to U.S. provisionalpatent application No. 62/373,751, entitled HIGH ALTITUDE BALLOONSYSTEMS AND METHODS and filed Aug. 11, 2016, and to U.S. provisionalpatent application No. 62/376,618, entitled HIGH ALTITUDE BALLOONSYSTEMS AND METHODS and filed Aug. 18, 2016, the disclosure of each ofwhich is hereby incorporated by reference herein in its entirety for allpurposes and forms a part of this specification.

BACKGROUND

Field

The technology relates generally to high altitude flight, in particularto systems and methods for lighter-than-air high altitude flight.

Description of the Related Art

High altitude flight, generally above about 50,000 feet, withlighter-than-air (LTA) systems is of interest for many applications,including communications, scientific research, meteorology,reconnaissance, tourism, and others. These and other applications imposestrict requirements on the LTA system. LTA systems can include balloonsystems in which a balloon envelope includes a lighter-than-air gas(e.g., helium or hydrogen).

SUMMARY

The embodiments disclosed herein each have several aspects no single oneof which is solely responsible for the disclosure's desirableattributes. Without limiting the scope of this disclosure, its moreprominent features will now be briefly discussed. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description” one will understand how the features of theembodiments described herein provide advantages over existing approachesto high altitude LTA flight.

Described herein are systems and devices for high altitude flight usinglighter-than-air (LTA) systems. The LTA systems and methods relate to aplatform having a tandem balloon system. A zero-pressure balloon (ZPB)is attached in tandem with a variable air super-pressure balloon (SPB).The ZPB provides lift for the system while the SPB provides a variableamount of ballast by pumping in or expelling out ambient air. Bydividing the two functions among the two separate balloons, each balloonand its associated accessories are configured for the respectiveballoon's particular function, allowing achievement of advancedperformance targets with the LTA. For instance, a compressor providesair to the SPB and can be configured for providing a sufficient rate andvolume of air at particular high altitudes in which the LTA system willbe flown. Such compressor designs allow for rapid descent, as well ashigh pressures within the SPB which allows for rapid venting and ascent,both of which can be performed at high altitudes. As further example,configurations of the SPB skin and accompanying tendons allow for astructurally efficient and stable SPB. For instance, the SPB may beconfigured to assume a “pumpkin” shape during flight capable ofwithstanding very large internal pressures, while also providingstability to prevent issues such as deformation of the skin, including“S-clefting.” These and other features of the LTA system provide theability to both simultaneously achieve high altitude (e.g. at or aboveabout 50,000 feet) and actively control altitude over a meaningful range(e.g. more than about 20,000 feet).

These and other features provide an LTA platform that can be scaled andconfigured simply for various missions and flight requirements. Forinstance, the basic design of the LTA system can be configured forhigher altitude and/or heavy lift missions with a higher capacitymulti-stage compressor and larger volume SPB and ZPB. As furtherexample, the LTA system can be configured for lower altitude and/orsmaller payload missions with a lighter weight system, for example witha single stage compressor and smaller volume SPB and ZPB. These andother features of the LTA systems described herein allow for performingadvanced maneuvers at high altitude with a scalable platform. Thus,further described herein are associated methods of navigation andcontrol with these LTA systems.

In one aspect, a lighter-than-air (LTA) high altitude balloon system isdescribed. The LTA system includes a zero-pressure balloon (ZPB), asuper-pressure balloon (SPB), a centrifugal compressor, an adjustablevalve, a sensor, a control system and a plurality of tendons. The ZPB isconfigured to receive therein an LTA gas to provide an upward liftingforce to the balloon system. The super-pressure balloon (SPB) has anouter skin and is configured to couple with the ZPB. The outer skindefines an interior volume configured to receive therein a variableamount of ambient air from a surrounding atmosphere to provide avariable downward force to the balloon system. The centrifugalcompressor is in fluid communication with the ambient air and with theinterior volume of the SPB. The centrifugal compressor is configured tocompress the ambient air and pump the compressed ambient air into theinterior volume of the SPB to increase the downward force to the balloonsystem. The adjustable valve is in fluid communication with the ambientair and with the interior volume of the SPB. The valve is configured tobe adjusted to release the compressed ambient air from the interiorvolume of the SPB to the surrounding atmosphere to decrease the downwardforce to the balloon system. The sensor is coupled with the balloonsystem and configured to detect an environmental attribute. The controlsystem is in communicating connection with the sensor, with thecentrifugal compressor, and with the adjustable valve. The controlsystem is configured to control the centrifugal compressor and theadjustable valve based at least on the detected environmental attributeto control the amount of compressed air inside the SPB to control analtitude of the balloon system. The plurality of tendons is coupled withthe SPB and extends along an exterior of the outer skin of the SPB. Theplurality of tendons is configured to bias the SPB into a pumpkin-likeshape at least when a first pressure inside the SPB is greater than asecond pressure of the surrounding atmosphere.

In some embodiments of the balloon system, the centrifugal compressorcomprises two or more stages. The centrifugal compressor may beconfigured to provide at least 500 liters of the ambient air per secondto the interior volume of the SPB at altitudes above 50,000 feet. Thecentrifugal compressor may be configured to provide the ambient air tothe interior volume of the SPB such that a resulting descent rate of theballoon system is at least 10,000 feet per hour at altitudes above50,000 feet. The resulting descent rate of the balloon system may be atleast 20,000 feet per hour.

In some embodiments of the balloon system, the adjustable valve isconfigured to be adjusted to release the pumped-in ambient air from theinterior volume of the SPB to the surrounding atmosphere such that aresulting ascent rate of the balloon system is at least 10,000 feet perhour at altitudes above 50,000 feet. The resulting ascent rate of theballoon system may be at least 20,000 feet per hour.

In some embodiments of the balloon system, the centrifugal compressorcomprises two or more stages and is configured to provide at least 500liters of the ambient air per second to the interior volume of the SPBsuch that a resulting descent rate of the balloon system is at least10,000 feet per hour at altitudes above 50,000 feet, and the adjustablevalve is configured to be adjusted to release the pumped-in ambient airfrom the interior volume of the SPB to the surrounding atmosphere suchthat a resulting ascent rate of the balloon system is at least 10,000feet per hour at altitudes above 50,000 feet.

In some embodiments of the high altitude balloon, the SPB comprises twoor more SPB compartments connected in series. The SPB may include two,three, four or more SPB compartments. The SPB compartments may beconnected in series and/or in parallel.

In some embodiments, the balloon system further comprises a payloadsupport, an elongated ladder assembly, and an air hose. The payloadsupport is coupled with the SPB and is configured to support a payload.The elongated ladder assembly couples the payload support with the SPBsuch that the payload support is located below the SPB when the balloonsystem is in flight. The air hose is fluidly coupled with thecentrifugal compressor, and the centrifugal compressor is mounted withthe payload support and is fluidly coupled with the interior volume ofthe SPB via the air hose. The air hose extends along and is supported atleast in part by the elongated ladder assembly.

In some embodiments, the payload support comprises a tetrahedral framecoupled with the SPB. In some embodiments, the payload support comprisesa tetrahedral frame coupled with the SPB and configured to support apayload.

In some embodiments, the balloon system further comprises a parafoilsystem coupled with the payload support and releasably coupled with theelongated ladder assembly in a stowed configuration, the parafoil systemconfigured to release from the elongated ladder assembly and to deployinto a deployed flight configuration to controllably descend with thepayload support to a landing site.

In some embodiments, the balloon system further comprises a solar arraythat includes one or more solar panels coupled with the elongated ladderassembly, wherein the elongated ladder assembly has a length based atleast in part on avoiding shading from the balloon system duringdaylight in order to provide sunlight to the one or more solar panels.

In some embodiments, the balloon system further comprises a gimbalrotatably coupling the ZPB with the SPB, the gimbal configured to rotatethe SPB relative to the ZPB, where the SPB and the solar array arerigidly coupled with the elongated ladder assembly such that rotation ofthe SPB with the gimbal rotates the elongated ladder assembly and thesolar array to a desired orientation.

In some embodiments, the balloon system further comprises one or morerelease lines and a tear line. The one or more release lines coupleupper and lower separable portions of the gimbal. The one or morerelease lines extend near a hot wire configured to be heated and therebyburn the one or more release lines. Burning the one or more releaselines separates the upper and lower portions of the gimbal. The tearline is coupled with the ZPB and with the lower portion of the gimbal.The tear line is configured to at least partially remove one or moregores of the ZPB due to separation and falling away of the lower portionof the gimbal from the ZPB.

In another aspect, a lighter-than-air (LTA) high altitude balloon systemis described. The balloon system comprises a zero-pressure balloon(ZPB), a super-pressure balloon (SPB), a multi-stage centrifugalcompressor and an adjustable valve. The ZPB is configured to receivetherein an LTA gas to provide an upward lifting force to the balloonsystem. The super-pressure balloon (SPB) is configured to couple withthe ZPB and to receive therein ambient air to provide a downward forceto the balloon system. The multi-stage centrifugal compressor isconfigured to pump the ambient air into the SPB to increase the downwardforce to the balloon system. The multi-stage centrifugal compressor isfurther configured to pump the ambient air into the SPB such that aresulting descent rate of the balloon system is at least 10,000 feet perhour at altitudes above 50,000 feet. In some embodiments, themulti-stage centrifugal compressor is thus configured for altitudesabove about 70,000 feet. The adjustable valve is configured to releasethe pumped-in ambient air from the SPB to decrease the downward force tothe balloon system. The adjustable valve is configured to release thepumped-in ambient air from the SPB such that a resulting ascent rate ofthe balloon system is at least 10,000 feet per hour at altitudes above50,000 feet. In some embodiments, the adjustable valve is thusconfigured for altitudes above about 70,000 feet. In some embodiments,the SPB is pumpkin-shaped at least when a first pressure inside the SPBis greater than a second pressure of a surrounding atmosphere

In another aspect, a method of controlling a lighter-than-air (LTA) highaltitude balloon system through a troposphere, tropopause andstratosphere is disclosed. The balloon system comprises a zero-pressureballoon (ZPB) coupled with a super-pressure balloon (SPB), a compressorfluidly coupled with the SPB and configured to pump ambient air into theSPB, and an adjustable valve fluidly coupled with the SPB and configuredto release the pumped-in ambient air from the SPB. The method comprisesdetermining a first range of latitude and longitude coordinatescorresponding to a first portion of the tropopause having a firstplurality of altitudes corresponding respectively to a first pluralityof wind directions within the tropopause. The method further comprisescontrollably releasing, with the adjustable valve, the ambient air fromthe SPB to ascend the balloon system from the determined first range oflatitude and longitude coordinates within the troposphere and throughthe tropopause to the stratosphere, where the balloon system travelsalong a first helical trajectory through the tropopause due to the firstplurality of wind directions at the first plurality of altitudes withinthe tropopause, where the balloon system ascends at a plurality ofascent rates through the tropopause, and where at least one of theplurality of ascent rates is at least 10,000 feet per hour. The methodfurther comprises determining a second range of latitude and longitudecoordinates corresponding to a second portion of the tropopause having asecond plurality of altitudes corresponding respectively to a secondplurality of wind directions within the tropopause. The method furthercomprises controllably pumping, with the compressor, the ambient airinto the SPB to descend the balloon system from the determined secondrange of latitude and longitude coordinates within the stratosphere andthrough the tropopause to the troposphere, where the balloon systemtravels along a second helical trajectory through the tropopause due tothe second plurality of wind directions at the second plurality ofaltitudes within the tropopause, where the balloon system descends at aplurality of descent rates through the tropopause, and where at leastone of the plurality of descent rates is at least 10,000 feet per hour.

In some embodiments of the method of controlling the balloon system, atleast one of the coordinates of the first range of latitude andlongitude coordinates is not within the second range of latitude andlongitude coordinates.

In some embodiments, the method further comprises travelling in agenerally horizontal first direction through the troposphere to one ofthe coordinates of the determined first range of latitude and longitudecoordinates before controllably releasing the ambient air to ascend theballoon system through the tropopause and into the stratosphere. In someembodiments, the method further comprises travelling in a generallyhorizontal second direction through the stratosphere to one of thecoordinates of the determined second range of latitude and longitudecoordinates after ascending to the stratosphere and before controllablypumping in the ambient air to descend the balloon system through thetropopause and into the troposphere. In some embodiments, the firstdirection is different from the second direction.

In some embodiments, the method further comprises maintaining theballoon system within a persistence envelope comprising portions of thetroposphere, tropopause and stratosphere. Maintaining the balloon systemwithin the persistence envelope comprises cyclically repeating thefollowing: travelling, from a starting position within the tropospherecorresponding to one of the coordinates of the second range of latitudeand longitude coordinates, along the generally horizontal firstdirection through the troposphere to a first location of the tropospherecorresponding to one of the coordinates of the first range of latitudeand longitude coordinates; ascending from the first location of thetroposphere through the tropopause along the first helical trajectory toa second location within the stratosphere; travelling along thegenerally horizontal second direction from the second location of thestratosphere to a third location of the stratosphere corresponding toone of the coordinates of the second range of latitude and longitudecoordinates; and descending from the third location of the stratospherethrough the tropopause along the second helical trajectory to an endingposition within the troposphere corresponding to one of the coordinatesof the second range of latitude and longitude coordinates.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. Understanding thatthese drawings depict only several embodiments in accordance with thedisclosure and are not to be considered limiting of its scope, thedisclosure will be described with additional specificity and detailthrough use of the accompanying drawings. In the following detaileddescription, reference is made to the accompanying drawings, which forma part hereof. In the drawings, similar symbols typically identifysimilar components, unless context dictates otherwise. The illustrativeembodiments described in the detailed description, drawings, and claimsare not meant to be limiting. Other embodiments may be utilized, andother changes may be made, without departing from the spirit or scope ofthe subject matter presented here. It will be readily understood thatthe aspects of the present disclosure, as generally described herein,and illustrated in the Figures, can be arranged, substituted, combined,and designed in a wide variety of different configurations, all of whichare explicitly contemplated and make part of this disclosure.

FIG. 1 is a perspective view of an embodiment of a lighter-than-air(LTA) system for high altitude flight including a zero-pressure balloon(ZPB), a super-pressure balloon (SPB) and a stratocraft having apayload, a parafoil descent system and supporting subsystems.

FIG. 2 is a perspective view of the ZPB of FIG. 1.

FIGS. 3A and 3B are, respectively, side and top views of the SPB of FIG.1.

FIGS. 4A and 4B are, respectively, side and top perspective views of anembodiment of a gimbal that may be used with the LTA system of FIG. 1.

FIGS. 4C and 4D are top perspective views of another embodiment of agimbal having a release mechanism that may be used with the LTA systemof FIG. 1.

FIGS. 5A and 5B are, respectively, perspective and side views of thestratocraft of FIG. 1 including embodiments of an upper craft having astowed parafoil and a payload support.

FIG. 5C is a close up view of a portion of a ladder assembly configuredto couple the payload support with the SPB such that the payload supportis located below the SPB when the balloon system is in flight.

FIG. 6 is a top perspective view of the payload support of FIGS. 5A-5Bincluding a compressor assembly.

FIGS. 7A and 7B are perspective views of the compressor assembly of FIG.6 shown in isolation from the payload support.

FIG. 8 is a perspective view of the parafoil system of FIGS. 5A and 5Bseparated from the LTA system and in a deployed flight configurationwith the payload support.

FIGS. 9A and 9B are side views of another embodiment of an LTA systemfor high altitude flight having a ZPB, an SPB and a compressor shown at,respectively, relatively lower and higher altitudes.

FIGS. 9C-9E are side views of other embodiments of LTA systems for highaltitude flight having a ZPB and either multiple SPB's or an SPBcomprising multiple compartments.

FIG. 10 is a schematic depicting an embodiment of a control system ofthe LTA system of FIG. 1 to control altitude and other parameters.

FIG. 11A is a schematic depicting embodiments of ascent and descentrates and flight ranges for the LTA of FIG. 1.

FIG. 11B is a flow chart showing an embodiment of a method for ascendingand descending with the LTA system of FIG. 1.

FIG. 12A is a schematic depicting an embodiment of a persistenceenvelope for high altitude station-keeping with the LTA system of FIG.1.

FIG. 12B is a flow chart showing an embodiment of a method forstation-keeping with the LTA system of FIG. 1.

DETAILED DESCRIPTION

The following detailed description is directed to certain specificembodiments of the development. Reference in this specification to “oneembodiment,” “an embodiment,” or “in some embodiments” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment is included in at least one embodiment of theinvention. The appearances of the phrases “one embodiment,” “anembodiment,” or “in some embodiments” in various places in thespecification are not necessarily all referring to the same embodiment,nor are separate or alternative embodiments necessarily mutuallyexclusive of other embodiments. Moreover, various features are describedwhich may be exhibited by some embodiments and not by others. Similarly,various requirements are described which may be requirements for someembodiments but may not be requirements for other embodiments.

Various embodiments will now be described with reference to theaccompanying figures, wherein like numerals refer to like elementsthroughout. The terminology used in the description presented herein isnot intended to be interpreted in any limited or restrictive manner,simply because it is being utilized in conjunction with a detaileddescription of certain specific embodiments of the development.Furthermore, embodiments of the development may include several novelfeatures, no single one of which is solely responsible for its desirableattributes or which is essential to practicing the invention describedherein.

One possible limiting factor for lighter-than-air (LTA) systems is theinability to effectively control the trajectory while in flight. Forinstance, some applications require the ability to ascend and descend atfast rates, to ascend and descend over large altitude ranges, tomaintain station-keeping envelopes for extended periods of time, tomaintain constellation coverage, etc. However, existing LTA systems donot provide simple and inexpensive solutions to achieve these and otheradvanced performance targets. There is, therefore, a need for such LTAsystems and methods. Embodiments of the present disclosure address theseand/or other challenges.

Described herein are systems and devices for high altitude flight usingLTA systems having tandem balloons. A zero-pressure balloon (ZPB) thatprovides lift is attached in tandem with one or more variable airballast super-pressure balloons (SPB). The SPB provides a controlled andvariable air ballast supply and emission (i.e. two-way ballast control)from ambient air in the surrounding atmosphere. A compressor, withsufficient air volume flow rate capabilities, provides sufficientambient air to the SPB even at low densities in high altitudes for rapiddescent or altitude maintenance. A controllable valve is sized andcontrolled for sufficient air release from the SPB for rapid ascent oraltitude maintenance. These and other features of the LTA system allowfor performance of advanced navigation and altitude control techniques.The LTA systems described herein are more agile, require less power andweigh less than existing balloon system solutions for similar missionrequirements. The LTA system thus allows for performance of advancedmaneuvers at high altitude, allowing for a multitude of high altitudeLTA system uses—and with a single, scalable platform. Described hereinare some embodiments of the LTA system and of some example methods ofusing the system, including rapid ascent/descent and station-keeping tomaintain a persistence envelope at high altitudes. Thus, the LTA systemhas various other embodiments and is capable of many other uses, even ifnot explicitly described herein.

As used herein, “high altitude” refers to altitudes that are in thestratosphere (above 35,000 feet), and includes without limitationaltitudes in the troposphere, the tropopause, and the stratosphere ofEarth's atmosphere. The altitude range for “high altitude”, for examplein terms of kilometers or miles, will vary depending on the latitude andlongitude. In some locations, high altitude will include a range ofabout 30,000 feet to about 120,000 feet or 130,000 feet. The exactaltitude of flight desired depends on the wind distribution and thetrajectory one is seeking. High altitude can also refer to altitudes ofnon-Earth atmospheres on other planets with atmospheres that may notfall within the given altitude range on Earth. Further, descriptionherein of a system as “high altitude” is not meant to exclude flight ofthat system through lower altitudes, for example during takeoff fromground and ascent to higher altitudes or descent and landing on theground.

A. LTA System

FIG. 1 is a perspective view of an embodiment of a lighter-than-air(LTA) system 100 for high altitude flight. For reference, a longitudinalaxis 105 is indicated. The longitudinal axis 105 is a reference axis fordescribing the system 100. Directions described as “outer,” “outward,”and the like, are referring to a direction at least partially away fromsuch longitudinal axes, while directions described as “inner,” “inward,”and the like, are referring to a direction at least partially towardsuch longitudinal axes.

For reference, a +Z direction is indicated that is opposite in directionto that of gravity, and a −Z direction is indicated that is opposite indirection to the +Z direction. For the sake of description, directionsdescribed as “upper,” “above,” and the like, are referring to adirection at least partially in the +Z direction, and directionsdescribed as “lower,” “below,” and the like, are referring to adirection at least partially in the −Z direction. The +Z direction isthe general direction the system 100 travels when ascending, while the−Z direction is the general direction the system 100 travels whendescending. The direction of ascent and descent of the system 100 maynot be aligned with, respectively, the +Z and −Z directions. Forexample, the system 100 may travel at an angle with respect to the +Zand −Z directions. Further, the longitudinal axis 105 may or may notalign with the +/−Z directions and/or with the direction of travel ofthe system 100.

The LTA system 100 is shown in flight. Various features of the system100 may change configuration, for example shape, geometry or dimensions,depending on the phase of a mission (e.g. takeoff, flight, landing).Thus, the depiction of the system 100 in any one configuration is notmeant to limit the disclosure to that particular configuration. Further,the basic design of the LTA system 100 may be adapted, for examplescaled, modularized, etc. for different mission requirements. The LTAsystem 100 can be modularized, for example with multiple SPB's 300 suchas in tandem pneumatically connected to each other, as furtherdescribed. The description herein is primarily of a very high altitudeand/or heavy payload lifting version of the LTA system 100, unlessotherwise stated. Therefore, other configurations, of the basic platformfor the particular LTA system 100 described herein, are within the scopeof this disclosure even if not explicitly described.

The LTA system 100 includes a zero-pressure balloon (ZPB) 200, asuper-pressure balloon (SPB) 300 and a stratocraft 400. The ZPB 200, SPB300 and the stratocraft 400 are shown coupled together. In some phasesof flight, the ZPB 200, SPB 300 and the stratocraft 400 are not coupledtogether. For example, portions of the stratocraft 400 may release fromthe LTA system 100, such as during descent of a payload and descentsystem. As further example, the ZPB 200, SPB 300 and/or the stratocraft400 may separate from each other after flight termination.

The ZPB 200 is a lifting balloon. The primary function of the ZPB 200 isto provide lift to the LTA system 100. A lighter-than-air (LTA) gas isprovided inside the ZPB 200 in an amount at launch sufficient for theLTA system 100 to take off. The ZPB 200 will initially be under-inflatedbut with sufficient lifting capacity in a collapsed configuration atlaunch from ground, and will expand as the LTA system 100 ascends tohigher altitudes with lower pressure air.

The ZPB 200 is a “zero-pressure” type of balloon. A “zero-pressureballoon” contains an LTA gas therein for providing lift to the LTAsystem 100. The ZPB 200 may be filled with helium or hydrogen. A“zero-pressure balloon” is normally open to the atmosphere via hangingor attached ducts to prevent over-pressurization. If flying alone as asingle ZPB 200, the ZPB 200 would be susceptible to the cyclic increaseand decrease in altitude caused by the constant balloon envelope volumechange due to heating and cooling, and therefore expansion andcontraction of the lift gas inside the ZPB 200 throughout the Earth'sdiurnal cycle. This constant altitude change leads to the loss of liftgas over time as the heating of the lift envelope during the day cyclecauses the lift gas to expand until the maximum float altitude isreached and the LTA gas is vented out of the opening in the ZPB 200.During the night cycle, the lift gas contracts, causing the ZPB 200envelop to contract and lose buoyancy. For this reason the LTA system100 controls the natural changes of buoyancy as well having the abilityto bias the buoyancy even more than simply neutralizing the naturalchanges in order to achieve controlled altitude changes. Particularembodiments and other aspects of the ZPB 200 are described in furtherdetail herein, for example with respect to FIG. 2.

The ZPB 200 supports the SPB 300. As shown, the SPB 300 is supportedunderneath the ZPB 200. The ZPB 200 may support the SPB 300 eitherdirectly or indirectly, for example via a rotatable actuator, asdescribed herein. Particular embodiments of rotatable connectionsbetween the ZPB 200 and SPB 300 are described in further detail herein,for example with respect to FIGS. 4A-4B.

The SPB 300 is a variable air ballast balloon. The primary function ofthe SPB 300 is to provide a variable amount of ballast to the LTA system100. Ballast is taken into the SPB 300 in the form of compressed air toprovide a greater downward force to the LTA system 100. Ballast isejected from the SPB 300 to provide a smaller downward force to the LTAsystem 100. The ballast is provided from the ambient atmospheric air,for instance by a compressor, as described in further detail herein, forexample with respect to FIGS. 6-7. To achieve neutral buoyancy the airballast can be set at some fraction of the SPB 300 maximum pressurecapability. This allows biasing in both a positive (greater air ballast)and negative direction (less air ballast) which leads to a descent speedor ascent speed respectively. In some embodiments, the LTA system 100includes only one SPB 300. However, the LTA system 100 can includemultiple SPB's 300, for example, two, three, four or more, as furtherdescribed herein, for example with respect to FIGS. 9C-9E.

The SPB 300 is a “super-pressure” type of balloon. A “super-pressureballoon” is completely enclosed and operates at a positive internalpressure in comparison to the external atmosphere. Pressure controlenables regulating the mass of air in the SPB 300, and therefore theoverall buoyancy of the LTA system 100. This buoyancy regulation enablesaltitude control of the LTA system 100. The SPB 300 may take in more airto apply more of a ballast force, for example to descend, or tocompensate for an expanding ZPB 200 that is producing more lift, asdescribed. Conversely, the SPB 300 may release air to apply less of aballast force, for example to ascend, or to compensate for a contractingZPB 200 that is producing less lift, as described. Particularembodiments and other aspects of the SPB 300 are described in furtherdetail herein, for example with respect to FIGS. 3A-3B.

The SPB 300 supports the stratocraft 400. As shown, the stratocraft 400is coupled with the SPB 300 beneath the SPB 300. The stratocraft 400 maybe directly or indirectly connected with the SPB 300. In someembodiments, there are various intermediate structures and/or systemsbetween the SPB 300 and the stratocraft 400, such as structuralconnectors, release mechanisms, other structures or systems, orcombinations thereof.

The stratocraft 400 includes one or more systems related to variousmission objectives. The stratocraft 400 may include the payload for aparticular mission. The stratocraft 400 may include various subsystems,such as power, control, communications, air intake, air release, payloaddescent, etc., for supporting a mission. Particular embodiments of thestratocraft 400 are described in further detail herein, for example withrespect to FIGS. 5A-5B. Some embodiments of particular payloads,supporting payload structures, air intake/release subsystems, andpayload descent subsystems, are described in further detail herein, forexample with respect to FIGS. 6-8.

B. Zero Pressure Balloon

FIG. 2 is a perspective view of the ZPB 200. ZPB 200 provides a liftforce in the +Z direction, as indicated. For reference, a geometriclongitudinal axis 205 of the ZPB 200 is indicated. The longitudinal axis205 may or may not align with the +Z direction, depending on the phaseof flight, environmental conditions, etc. Further, the ZPB 200 may notcause the LTA system 100 to travel exactly in the +Z direction. Thus,while the lift force is in the +Z direction, the LTA system 100 may nottravel in that same direction. In some embodiments, the LTA system 100ascends in a direction that is at an angle to the +Z direction.

The ZPB 200 includes an upper portion 210 having a top 212 and a lowerportion 215 having a bottom 217. The upper portion 210 refers to a partof the ZPB 200 that is above the lower portion 215. The upper and lowerportions 210, 215 may be the upper and lower halves of the ZPB 200. Theupper and lower portions 210, 212 may be symmetric about thelongitudinal axis 205, for example when the ZPB 200 is fully inflated atits maximum volume altitude, such as in higher altitudes with less densesurrounding atmosphere. The dimensions of the ZPB 200 when upright andfully inflated may be about 100 feet wide and about 95 feet high. TheZPB 200 may have a range of widths from about 75 feet or less to about370 feet or more. The ZPB 200 may have a range of heights from about 70feet or less to about 310 feet or more.

The ZPB 200 includes a skin 220. The skin 220 forms the upper and lowerportions 210, 215 of the ZPB 200, or sections thereof. The skin 220 isassembled to form the outer body of the ZPB 200. The skin 220 may beabout 0.0008 inches thick. Various versions of the ZPB 200 may have arange of thicknesses of the skin 220 from about 0.00025 inches or lessto about 0.0015 inches or more thick. The skin 220 may have a generallyuniform thickness over most or all of the ZPB 200. In some embodiments,the thickness of the skin 220 may vary depending on the location of theskin 220 about the ZPB 200. The basic skin is known as the “shell”, andif extra thickness is required for structurally containing the liftbubble at launch, those extra layers are known as “caps”. Caps areusually some fraction of the gore length covering the top of the shelland usually are no longer than 50% of the gore length, although thischanges depending on the design altitude.

The skin 220 defines one or more interior compartments of the ZPB 220for receiving an LTA. In some embodiments, the ZPB 200 is configured toreceive therein an LTA gas to provide an upward lifting force to the LTAsystem 100. The ZPB 200 may include about 500,000 cubic feet of maximuminternal volume. Various versions of the ZPB 200 may include a rangefrom about 250,000 cubic feet or less to about 30,000,000 cubic feet ormore of maximum internal volume. The ZPB 200 may include sufficient liftgas to lift the gross weight of the vehicle plus additional “free lift”which can range from 5% of the gross weight to about 25% of the grossweight depending on the application. The volume of the launch “bubble”is a fraction of the maximum design volume and usually ranges from 1/20to 1/200 of design volume depending on design altitude.

The skin 220 may be formed from a variety of materials. In someembodiments, the skin 220 is formed from plastic, polymer, thin films,other materials, or combinations thereof. The skin 220 may be made frommultiple components. As shown, the skin 220 includes gores 225. The skin220 may be configured with gores 225, other suitable approaches, orcombinations thereof. The gores 225 are elongated sections of balloonmaterial. The gores 225 may extend to the top 212 and/or to the bottom217. In some embodiments, the gores 225 do not extend to the top 212and/or to the bottom 217. For example, the skin 220 may be formed ofgores 225, with endcaps surrounding upper and lower ends of the gores225 at the top 212 and/or bottom 217. In some embodiments, the bottom217 of the ZPB 200 is open and the lower ends of the gores 225 extend toor near the opening formed at the bottom 217.

The ZPB 200 changes configuration (shape, size, etc.) during flight asthe lift gas volume expands and contracts. The skin 220 or portionsthereof may change configuration due to launch requirements, variableair pressure, changes in volume of LTA, release of payload and descentsystems, flight termination, etc.

C. Super Pressure Balloon

FIGS. 3A and 3B are, respectively, side and top views of the SPB 300.The SPB 300 provides a downward ballast force in the −Z direction, asindicated. For reference, a geometric longitudinal axis 305 of the SPB300 is indicated. The longitudinal axis 305 may or may not align withthe −Z direction, depending on the phase of flight, environmentalconditions, etc. Further, the SPB 300 may not cause the LTA system 100to travel exactly in the −Z direction. Thus, while the downward force isin the −Z direction, the LTA system 100 may not travel in that samedirection. In some embodiments, the LTA system 100 descends in adirection that is at an angle to the −Z direction, which may be mostlydue to wind. In some embodiments, the force due to lift from the ZPB 200is greater than the combined downward force due to gravity exerted bythe entire LTA system 100, including the weight of the ZPB 200, theweight of the SPB 300, the weight of the stratocraft 400, etc. such thatthe LTA system 100 ascends in a direction that is at least partially inthe +Z direction. In some embodiments, the force due to lift from theZPB 200 is less than the combined downward force due to gravity exertedby the entire LTA system 100, including the weight of the ZPB 200, theweight of the SPB 300, the weight of the stratocraft 400, etc. such thatthe LTA system 100 descends in a direction that is at least partially inthe −Z direction.

The SPB 300 includes an upper portion 310 having a top 312 and a lowerportion 315 having a bottom 317. The upper portion 310 refers to a partof the SPB 300 that is above the lower portion 315. The upper and lowerportions 310, 315 may be the upper and lower halves of the SPB 300. Theupper and lower portions 310, 312 may not be separate parts, but may beportions of the same continuous skin of the SPB 300 used for descriptionherein. The upper and lower portions 310, 312 may be symmetric about thelongitudinal axis 305, for example when the SPB 300 is fully inflatedwhen pressurized, which may be in higher altitudes with less denseatmosphere. The axis 305 of the SPB 300 may align with and/or beparallel to the axis 205 of the ZPB 200. In some embodiments, the axis305 of the SPB 300 may not align with and/or not be parallel to the axis205 of the ZPB 200. In some embodiments, the axis 305 of the SPB 300 mayalign with and/or be parallel to the axis 205 of the ZPB 200 during somephases of a flight, and the axis 305 of the SPB 300 may not align withand/or not be parallel to the axis 205 of the ZPB 200 during otherphases of a flight.

The maximum dimensions of the SPB 300, for example when fully inflated,may be about 56 feet wide in diameter and about 35 feet long in height.The SPB 300 may have a range of maximum diameters from about 10 feet orless to about 500 feet or more. The SPB 300 may have a range of maximumlengths from about 5 feet or less to about 300 feet or more.

The SPB 300 includes a skin 320. The skin 320 forms the upper and lowerportions 310, 315 of the SPB 300, or sections thereof. The skin 320 isassembled to form the outer body of the SPB 300. The skin 320 may beabout 0.004 inches thick. Various versions of the SPB 300 may have arange of thicknesses of the skin 220 from about 0.0015 inches to about0.008 inches thick. The skin 320 has a generally uniform thickness overmost or all of the SPB 300. In some embodiments, the thickness of theskin 320 may not be uniform and may vary depending on the location ofthe skin 320 about the SPB 300.

The skin 320 defines one or more interior compartments of the SPB 300for receiving and storing ambient air. In some embodiments, the outerskin 320 defines an interior volume of the SPB 300 configured to receivetherein a variable amount of ambient air from a surrounding atmosphereto provide a variable downward force to the LTA system 100. The SPB 300may have a maximum internal volume of about 64,000 cubic feet. Variousversions of the SPB 300 may include a range from about 32,000 cubic feetor less to about 90,000 cubic feet or more of maximum internal volume.

The skin 320 may be formed from a variety of materials. In someembodiments, the skin 320 is formed from plastic, polymer, thin films,other materials, or combinations thereof. The skin 320 may be made frommultiple components. As shown, the skin 320 includes gores 325. The skin320 may be configured with gores 325, other suitable approaches, orcombinations thereof. The gores 325 are elongated sections of balloonmaterial. The gores 325 may extend to the top 312 and/or to the bottom217. In some embodiments, the gores 325 do not extend to the top 312and/or to the bottom 317. For example, the skin 320 may be formed ofgores 325, with endcaps surrounding upper and lower ends of the gores325 at the top 312 and bottom 317.

The SPB 300 includes multiple tendons 330. The tendons 330 are elongatedflexible members. The tendons 330 may be axially-stiff,transverse-flexible rope-like members. The tendons 330 may be formed offiber, composites, plastic, polymer, metals, other materials, orcombinations thereof. The tendons 330 may have a denier of about 61,000.The tendons 330 may have range of deniers from about 10,000 to about200,000. The tendons 330 may have a thickness of about 0.125 inch. Thetendons 330 may have a thickness of 0.125 inch. The tendons 330 may haverange of thicknesses from about 0.05 inches or less to about 0.5 inchesor more. The tendons 330 may include covers or sheaths, either partiallyor entirely. The tendons 330 extend along the outside of the skin 320.The tendons 330 may extend from or near the top 312 to or near thebottom 317 of the SPB 300. The tendons 330 are meridonially configured,extending meridonially along the SPB 300. The tendons 330 may beseparate from each other. In some embodiments, some or all of thetendons 330 may be coupled together. In some embodiments, some or all ofthe tendons 330 may form one continuous, long tendon. In someembodiments, the LTA system 100 includes a plurality of the tendons 330coupled with the SPB 300 and extending along an exterior of the outerskin 320 of the SPB 300 and configured to bias the SPB 300 into apumpkin-like shape at least when the SPB 300 is pressurized relative tothe surrounding atmosphere, for instance when a first pressure insidethe SPB 300 is greater than a second pressure of the surroundingatmosphere.

The SPB 300 may include tape 335. The tape 335 may be an adhesivematerial. The tape 335 may couple sections of the skin 320, such as thegores 325, together. The tape 335 may extend along edges of the gores325. The tape 325 may extend underneath or generally near the tendons330. In some embodiments, a segment of tape 325 extends underneath acorresponding segment of tendon 335. The tape 335 may extend to or nearthe top 312 and/or to or near the bottom 317 of the SPB 300.

The SPB 300 changes configuration (shape, size, etc.) during flight. Theskin 320, tendons 330, and/or tape 335, or portions thereof, may changeconfiguration due to launch requirements, variable air pressure, changesin volume of LTA, release of payload and descent systems, flighttermination, pressurization with a compressor, etc. In some embodiments,the SPB 300 may be configured to take a particular shape during flight,such as a “pumpkin” shape or other shapes, as described herein.

The SPB 300 is shown with bulges 340. The bulges 340 are portions of theskin 320 that are located farther outward than adjacent portions of theskin 320. For example, the bulges 340 may be curved portions of thegores 325 that are located farther radially from the longitudinal axis305 than adjacent portions of longitudinal edges of the gores 325. Thebulges 340 may refer to portions of the skin 320 that are locatedfarther outward than adjacent tendons 330 and/or tape 335. The bulges340 may assist with forming part of the pumpkin shape of the SPB 300.This is a natural structural result of pressurizing the film while in ameridionally-reinforced multi-gore configuration.

The SPB 300 may be configured based on maximization of a performanceratio R defined by R=[ΔP×V]/M. Here, “ΔP” is the differential pressurebetween the internal pressure of the SPB 300 and the ambient pressure ofthe immediately surrounding atmosphere, “V” is the maximum internalvolume of the SPB 300 when assuming an inflated shape, and “M” is thegross mass of the LTA system 100 structure (e.g. the total mass of theZPB 200, the SPB 300, the stratocraft 400, and other structural featuresof the LTA system 100, but not including the mass of any internal air orlift gas in the various balloons). In some embodiments, ΔP is about 3500Pa. In some embodiments, ΔP is 3500 Pa, 5000 Pa, 7500 Pa, 10,000 Pa, or12,000 Pa. Depending on the embodiment, ΔP may be within a range fromabout 750 Pa or less to about 12,000 Pa or more. In some embodiments, Vis as described above regarding the internal volume of the SPB 300. Insome embodiments, M is about 600 kilograms. Depending on the embodiment,M may be within a range from about 125 kilograms or less to about 2,000kilograms or more.

The performance ratio R may be maximized with various configurations ofthe system 100. For example, the “Pumpkin” configuration of the SPB 300,as further described herein, allows for a large “ΔP” and “V” with asmaller “M,” which increases the ratio “R.” As further example, anefficient intake and release of air allows for quickly filling the large“V” to perform the advanced maneuvers and missions. Features forachieving such efficient intake and release of air are described infurther detail herein, for example with respect to FIGS. 6-7.

The SPB 300 may be in a “pumpkin” shape. The pumpkin shape may includethe multiple bulges 340, a flattened top 312, a flattened bottom 317,and/or non-circular lateral cross-sections of the skin 320 (i.e.cross-sections of the skin 320 taken along a plane that includes thelongitudinal axis 350). The skin 320 and accessories such as the tendons330, tape 335, etc. may be designed to achieve the pumpkinconfiguration.

The SPB 300 may be designed to withstand large internal pressures whilealso providing structural stability at such large pressures. As furtherdiscussed herein, larger internal pressures of the SPB 300 allow forperforming advanced maneuvers and achieving advanced mission goals withthe system 100. However, large internal pressures of the SPB 300 maycause problems with structural integrity, stability, etc. For instance,“S-clefting” is a serious global geometric shape instability to whichpumpkin-shaped balloons are susceptible. S-clefting can result in theskin 320 locally buckling and bunching together along a continuous curvefrom top to bottom, resulting in the general shape of an “S” on theballoon's surface. S-clefting may be caused by an excess of skin 320material in the equatorial region, for example in the middle portion311. The pumpkin shape may contribute to such concentration of material,for instance by having a well-rounded bulge-lobe angle. To imagine whatis meant by bulge angle, consider a circle. Draw a line from a point onthe circle to the center, then back out to another point on the circlenot too far away from the first point. The angle of the “V” that wasjust drawn is the bulge angle, and the arc between the two pointsrepresents the shape of the gore bulge, or lobe. The reason to have thewell-rounded bulge 340 (small bulge radii) is that it lowers the hoopstress in the skin 320 which allows for higher differential pressures inthe SPB 300 without reaching the burst point. For instance, the pressureloads may be more efficiently transferred to the tendons 330, which mayextend along the valleys 342 between the bulges 340. This beneficialstress-lowering effect however has a limit where too much material leadsto the s-cleft instability.

The S-cleft depends in part on the number of gores 325 and the flatnessof the bulges 340. “Flat” here refers to a smaller radial distancebetween the outermost and innermost portions of a given bulge 340(smaller bulge angle). Flatter bulges 340 reduce the concentration ofmaterial around the balloon's middle portion 311 thus reducing theS-cleft susceptibility, but they also increase the hoop stress thusreducing the internal pressure capability. Further, a greater number ofgores 325 reduces the load per tendon, but increases the S-cleftsusceptibility. Thus, the number of gores 325, the flatness of thebulges 340, and the overall “pumpkin” shape are configured so the SPB300 can withstand a high internal pressure while preventing structuralinstabilities such as S-clefting. The skin thickness, the designdifferential pressure, the arc angle of the gore bulges (“bulge angle”),strength and stiffness of the tendons, and the number of gores (andtherefore number of tendons) have to be carefully balanced in the designprocess to not exceed the strength of the structural elements and to nothave global shape instabilities called “s-clefts”.

D. Rotatable Actuator

FIGS. 4A and 4B are perspective views of an embodiment of a gimbal 500that may be used with the LTA system 100. The ZPB 200 and SPB 300 may becoupled together directly or indirectly, as mentioned. As shown in FIG.4A, the ZPB 200 and SPB 300 are coupled together indirectly via thegimbal 500. The gimbal 500 is coupled, for example structurallyattached, with the bottom 217 of the ZPB 200 and the top 312 of the SPB300. The gimbal 500 provides for rotation of the SPB 300 relative to theZPB 200 about the longitudinal axis 105. In some embodiments, the gimbal500 may provide for rotation about an axis that is not aligned and/orparallel to the longitudinal axis 105. Further, the gimbal 500 may be arotatable actuator configured for rotation about more than one axis.

The gimbal 500 may be coupled with various features of the respectiveballoons. As shown in FIG. 4B, the gimbal includes a lower bracket 502attached to a plate 314 of the SPB 300. The top 312 of the SPB 300includes the plate 314 attached to an apex of the SPB 300. The apex 313may be a portion of the skin 320 at the top 312 of the SPB 300. Theplate 314 is a structural fitting attached to the apex 313. The lowerbracket 502 of the gimbal 500 is attached to the plate 314 via fasteners504, such as bolts. Other suitable connectors, in addition oralternatively to fasteners 504, may be used. The gimbal 500 may alsoinclude standoffs 506. The standoffs 506 are structural separators thatprovide spacing between the gimbal (e.g. the lower bracket 502) and theSPB 300 (e.g. the plate 314). There may be a series of the fasteners 504and/or the standoffs 506 in various locations.

The gimbal 500 may include a motor 510. The motor 510 causes movement ofportions of the gimbal 500. The motor 510 may be a variety of differentsuitable motion actuators. In some embodiments, the motor 510 is anelectric, combustion, or other type of motor. The motor 510 may outputrotation at a speed of about 5 rpm. Depending on the embodiment, themotor 510 may output rotation within a range of about 1 rpm or less toabout 20 rpm or more. The motor 510 may be reversible. For instance, themotor 510 may be configured to cause movement in a first direction andin a second direction that is opposite the first direction. In someembodiments, the motor 510 can rotate clockwise as well ascounterclockwise.

The gimbal 500 further includes a first gear 515. The first gear 515 isrotated by the motor 510. The first gear 515 may be rotatably mounted onan end of an axle of the motor 510. The gimbal 500 further includes asecond gear 520. The second gear 515 is rotatably coupled with the lowerbracket 502. The second gear 520 is in mechanical communication with thefirst gear 515, such that rotation of the first gear 515 causes rotationof the second gear 520. The second gear 520 may have a larger diameterthan the first gear 515. The first and second gears 510, 520 may becircular as shown. The first and second gears 510, 520 may be formedfrom various suitable materials, such as metals, other materials, orcombinations thereof.

The gimbal 500 may include one or more connectors 525. As shown, theremay be three connectors 525. The connectors 525 are structuralconnections. As shown, the each connector 525 may have an elongatedmember 527 with attachments 529 on upper and lower ends of the connector525. The elongated member 527 may have a cylindrical cross-section. Theattachments 529 on the lower end of the connector 525 connect with thesecond gear 520. Rotation of the second gear 520 moves the connectors525 along a corresponding circular path. The attachments 529 on theupper end of the connectors 525 connect with an upper bracket 530. Theupper bracket 530 is a structural attachment, and may be formed from avariety of suitable materials, including metals, other materials, orcombinations thereof. The upper bracket 530 couples with the ZPB 200.For example, the upper bracket 530 may be structurally attached,directly or indirectly, to the bottom 217 of the ZPB 200, usingfasteners, etc.

The connectors 525 may assist with dynamic stability of the system 100.For example, the ZPB 200, SPB 300 or other parts of the system 100 (e.g.the stratocraft 400) may be more susceptible to, or subject to, adisturbance, such as a wind gust, weather, or other environmentalfactors. The connectors 525 may assist with compensating for anyresulting movement of the SPB 300 relative to the ZPB 200. Theconnectors 525 may provide such flexibility in any direction, includingaxially in the +/−Z direction, at an angle to the +/−Z direction, etc.

The connectors 525 may assist with lateral stiffness of the system 100by providing a flexible or moveable connection between the ZPB 200 andthe SPB 300. In some embodiments, the connectors 525 or portions thereofmay be formed from flexible materials, such as metals, composites, othersuitable materials, or combinations thereof. In some embodiments, themember 527 of each connector 525 is formed from such flexible materials.In some embodiments, the connectors 525 may have flexible attachmentswith the gimbal 500 and/or the ZPB 200 allowing for some movement. Forinstance, the attachments 529 may allow for rotation of the attachments529 relative to the upper bracket 530 and/or second gear 520 aboutparticular axes, for example about axes not aligned with the axis ofrotation of the gimbal 500. As further example, the members 527 may berotatably coupled with the corresponding attachments 529 for thatconnector 525. This may allow for relative rotation between the members527 and the attachments 529. These and other features may assist withisolating undesirable relative movement between the ZPB 200 and the SPB300, while allowing for desirable rotation of the SPB 300, as describedherein.

Rotation of the gimbal 500 causes relative rotation between the ZPB 200and the SPB 300. Rotation of the SPB 300 may be desirable for pointing asolar array 630, as further described herein, for example with respectto FIGS. 5A-5B. For example, the gimbal 500 may be configured to rotatethe SPB 300 relative to the ZPB 200, wherein the SPB and the solar array630 are rigidly coupled with an elongated ladder assembly 610 such thatrotation of the SPB 300 with the gimbal 500 rotates the elongated ladderassembly 610 and the solar array 630 to a desired orientation. In someembodiments, the gimbal 500 has sufficient torsional stiffness andcontrol authority to point the payload support 700 (e.g., via rotationof the SPB 300 that is coupled with the payload support 700) in adesired direction and maintain that directional pointing despite naturalor induced atmospheric disturbances to or flows over the LTA system 100.

In some embodiments, both the ZPB 200 and the SPB 300 rotate uponactuation of the gimbal 500. The ZPB 200 and the SPB 300 may rotate inopposite directions upon actuation of the gimbal 500. In someembodiments, the gimbal 500 may be rigidly coupled with both the ZPB 200and the SPB 300 such that rotation of the gimbal 500 is transmitted toboth the ZPB 200 and the SPB 300. The couplings between the gimbal 500and the ZPB 200 and the SPB 300 may allow for rotation about thelongitudinal axis 105. In some embodiments, the gimbal 500 may includethe flexible connectors 525 and/or rotatable connections between themembers 527 and attachments 529, as described above, for dynamicstability but still allow for rotation about the longitudinal axis 105.

The gimbal 500 may cause relative rotation of the ZPB 200 and the SPB300 at various speeds. In some embodiments, the gimbal 500 causesrelative rotation of the ZPB 200 and the SPB 300 at a speed of about 24degrees per second. Depending on the embodiment, the gimbal 500 maycause relative rotation of the ZPB 200 and the SPB 300 within a range ofspeeds from about 1 degree per second or less to about 96 degrees persecond or more.

The gimbal 500 may prevent or mitigate rotation of the SPB 300 relativeto the ZPB 200. For example, the gimbal 500 may be locked so that norotation is transmitted. In some embodiments, the first gear 515 may belocked such that the second gear 520, which is in mechanicalcommunication with the first gear 515, is also prevented from moving. Asfurther example, the gimbal 500 may be locked and automatically unlockupon application of a threshold force. In some embodiments, the motor510 may allow for rotation if a rotational force is transmitted to thefirst gear 515. For instance, disturbances to the system 100 may causethe ZPB 200 to rotate relative to the SPB 300. If such disturbancestransmit large rotational forces to the gimbal 500, the gimbal 500 mayallow for such rotations to prevent structural failure to the gimbal500. For example, the motor 510 may be locked but allow for rotation ofthe first gear 515 upon application of a threshold rotational force,which may prevent damage to the first or second gears 515, 520, or toother components of the system 100.

The gimbal 500 may include a tear line 535. The tear line 535 comprisesa rope, wire or other structural connector that connects the gimbal 500,or portions thereof, to one or more gores of the ZPB 200. One end of thetear line 535 may be connected to one of the attachments 529 and theopposite end of the tear line 535 may be connected to the ZPB 200, suchas one of the gores 225 at or near the upper portion 210 of the ZPB 200.The tear line 535 may facilitate “goring” of the ZPB 200 for flighttermination, as described herein. For example, at the end of a mission,the gimbal 500 and SPB 300 may detach from the ZPB 200, and the fallinggimbal 500 and SPB 300 may cause the tear line 535 to rip one or more ofthe gores 225, and/or other portions of the skin 220, from the ZPB 200.By tearing the gores 225, the lift gas of the ZPB 200 will escape to theatmosphere, causing the ZPB 200 to fall to ground. Further details ofthe tear line 535 are described herein, for example with respect toFIGS. 4C and 4D.

FIGS. 4C and 4D are top perspective views of another embodiment of agimbal 501 that may be used with the LTA system 100. The gimbal 501 mayhave all or some of the same or similar features and/or functionalitiesas the gimbal 500, and vice versa. Thus, for example, the gimbal 501 maycouple the ZPB 200 to the SPB 300, provide for rotation of the SPB 300relative to the ZPB 200, etc. Further, the gimbal 501 includes a releasemechanism 503. The release mechanism 503 provides for separation of theSPB 300 from the ZPB 200 in flight, for example at high altitudes. Therelease mechanism 503 may provide for the gimbal 501, or portionsthereof, to release from the ZPB 200. In some embodiments, the gimbal501, or portions thereof, may be attached to the SPB 300 after actuationof the release mechanism 503. The release mechanism 503 may also providefor termination of flight of the ZPB 200 and/or SPB 300, for example bygoring the ZPB 200, as described herein.

The release mechanism 503 includes one or more release lines 526. Asshown, there are three release lines 526. There may be fewer or morethan three release lines 526, for example one, two, four, five, six,seven, eight, nine, ten or more release lines 526. Each release line 526is a burn wire. The release lines 526 will split into two or moreportions upon application of sufficient heat. The release lines 526 maybe formed from a variety of materials, including fabrics, metals,alloys, composites, fibers, nichrome, other suitable materials, orcombinations thereof. The size of the release lines 526, for examplethickness, may be chosen based on a variety of parameters, includingmass of the LTA system 100 or portions thereof, the amount of heat to beapplied to the release lines 526, environmental conditions during flightand upon actuation of the release mechanism 503, etc.

The release lines 526 couple together upper and lower portions of thegimbal 501. As shown, the release lines 526 couple together the upperbracket 530 and the second gear 520. The release lines 526 may coupletogether other portions of the gimbal 501. In some embodiments, therelease lines 526 may couple together other portions of the LTA system100, such as portions of the gimbal 501 and the ZPB 200 or SPB 300. Therelease lines 526 releasably couple together the various portions. Therelease lines 526 may thus provide for release or separation of thevarious portions of the LTA system 100 coupled together, for example byburning and separating of the release lines 526. As shown, the releaselines 526 provide for release of the upper portion of the gimbal 501,including among other things the upper bracket 530, from the lowerportion of the gimbal 501, including among other things the second gear520.

The release lines 526 may thus attach opposing portions of the gimbal501. The release lines 526 attach to the attachments 529 at the upperportion of the gimbal 501. The release lines 526 extend from these upperattachments downward to respective guides 528. The guides 528 areattached to the second gear 520. The guides 528 may be attached to otherstructures, such as an intermediate attachment between the second gear520 and the guides 528. The guides 528 are shown as U-bolts fixedlyattached to the second gear 520. The guides 528 define openings 531through the guides 528. The openings 531 are spaces of the guides 528through which the release lines 526 extend. The release lines 526 maywrap over and through the guides 528. The release lines 526 may wrapover the guides 528 once, as shown. In some embodiments, the releaselines 526 may wrap around the guides 528 one or more times beforeextending away from the guides 528. The guides 528 and openings 531thereof provide for a smooth, rounded surface over or around which therelease lines 526 wrap. The rounded portions of the guides 5289 may besized to reduce stress, wear, etc. on the release lines 526. The releaselines 526 extend from the guides 528 to opposing lower attachments 529of the gimbal 501. The lower attachments 529 are attached to the secondgear 520 opposite the respective guide 528. The release lines 526 arefixedly attached to the lower attachments 529. As shown, the releaselines 526 approach and exit the guides 528 at slightly more than aninety degree angle. The release lines 526 may be oriented in a varietyof other orientations. The release lines 526 extend from a respectiveguide 528 and over a separator assembly 534.

The release lines 526 may include burn portions 532 that extend over theseparator assembly 534. The burn portions 532 are portions of therelease lines 526 that separate upon application of heat from theseparator assembly 534. The burn portions 532 may be one or more regionsof the release lines 526. The burn portions 532 may include the materialthat separates upon application of heat. The entire release line 526 maybe made of the same material as the burn portion 532. In someembodiments, the burn portion 532 may be made of different material asthe remaining portions of the release line 526. For example, the burnportion 532 may include a burnable material while the remainder of therelease line 526 may not be burnable. The burn portion 532 may extendfrom a respective guide 528 to an opposing lower attachment 529. Theburn portion 532 may be a smaller portion that only is adjacent theseparator assembly 534.

A close up view of the separator assembly 534 is shown in FIG. 4D. Theseparator assembly 534 provides for separation of the release lines 526.The separator assembly 534 may separate the burn portions 532 of therelease lines 526 that extend from the guides 528 to opposing lowerattachments 529. The release lines 526 may extend over the separatorassembly 534 as shown. In some embodiments, the release lines 526 mayextend through, around, in, under, etc. the separator assembly 534.

The separator assembly 534 is mounted on a protrusion 536. Theprotrusion is part of the second gear 520. The protrusion 536 may be aseparate part from the second gear 520 that is attached to the secondgear 520. The protrusion 536 supports the separator assembly 534. Theseparator assembly 534 includes a nut castle 538. The nut castle 538 ismounted on the protrusion 536. The nut castle 538 may releasably attachto the protrusion 536. In some embodiments, the nut castle 538threadingly engages with, for example screws into, the protrusion 536and/or other portions of the second gear 520. The nut castle 538provides for securement of various features of the separator assembly534. The nut castle 538 may provide for extension therethrough ofvarious electrical wires, heating elements, burn mechanisms, etc. Theseparator assembly 534 may rotate with the SPB 300. For example, theseparator assembly may be attached to the SPB 300 such that rotation ofthe SPB 300 will rotate the separator assembly 534. The separatorassembly 534 may therefore rotate relative to the release lines 526.Rotation of the separator assembly 534 may distribute thermal energy,for example from a hot wire 544 as further described, over a widerportion of the burn portions 523 of the release lines 526.

The separator assembly 534 includes a hot wire plug 540. The hot wireplug 540 is secured by the nut castle 538. The hot wire plug 540 may bethreadingly engaged with the nut castle 540 or otherwise suitablysecured with the nut castle 538. The hot wire plug 540 is connected withan electrical current source, for example a battery, to provide electriccurrent to one or more hot wire engagements 542. The battery may belocal to the gimbal 501. In some embodiments, the battery may be locatedwith other portions of the LTA system 100, for example with the payloadsupport 700, and having wires extending from the payload support 700along the ladder assembly 610 and around or through the SPB 300. The hotwire engagements 542 couple with the hot wire plug 540. The hot wireengagements 542 when connected with the hot wire plug 540 are inelectrical communication with the electrical current source.

The hot wire engagements 542 are electrically connected to the hot wire544. The hot wire 544 thus receives electric current from the electriccurrent source. The hot wire 544 heats up upon receipt of electriccurrent therethrough. The hot wire 544 may be formed from a variety ofsuitable materials, such as metals, alloys, fibers, high electricalresistance materials, other suitable materials, or combinations thereof.The hot wire 544 may extend from a first hot wire engagement 542 to asecond hot wire engagement 542. Current may flow from the first hot wireengagement 542, through the hot wire 544 and to the second hot wireengagement 542. The hot wire 544 extends in a coil shape as shown. Insome embodiments, the hot wire 544 may have other shapes besides a coil.The hot wire 544 forms the coil between the hot wire engagements 542.The coil formed by the hot wire 544 may include multiple loops as shown.In some embodiments, the coil formed by the hot wire 544 may only be oneloop. The coil may be various sizes, for example various diameters andlengths, depending, for example, on the size of the burn portions 532 ofthe release lines 526, on the proximity of the hot wire 544 to the burnportions 532, on the amount of current applied to the hot wire 544, onthe amount of heat generated by the hot wire 544, etc. The coil formedby the hot wire 544 is shown as generally horizontal. In someembodiments, the coil formed by the hot wire 544 may be at otherorientations, for example angled, vertical, etc. In some embodiments,there may be multiple coils formed by the hot wire 544.

The hot wire 544 heats up and transfers heat to the release lines 526.The hot wire 544 transfers heat to adjacent and/or contacting portionsof the release lines 526. The hot wire 544 transfers heat to the burnportions 532 of the release lines 532. The transferred heat causes theburn portions 532 to burn and thereby separate. The burn portions 532may be positioned adjacent to the hot wire 544. As shown, the burnportions 532 extend over the hot wire 544. The burn portions 532 mayextend through, around, under, etc., the hot wire 544. In someembodiments, the burn portions 532 may extend through the coil formed bythe hot wire 544. In some embodiments, the burn portions 532 maypartially extend adjacent to the hot wire 544 and partially extendthrough the coil formed by the hot wire 544. In some embodiments, theburn portions 532 may contact the hot wire 544. The hot wire 544includes a single burn region, e.g. the coil, that causes multiple burnportions 532 of the release lines 526 to separate. In some embodiments,there may be multiple burn regions, for example multiple coils, thatcause multiple burn portions 532 of the release lines 526 to separate.Thus, the configuration shown is merely one example and many othersuitable configurations may be implemented.

The separator assembly 534 or portions thereof may rotate with the SPB300. Rotation of the separator assembly 534 may distribute thermalenergy over a wider part of the burn portions 532. For example, the burnportions 532 may extend over the coiled hot wire 544 and rotation of thehot wire 544 relative to the burn portions 532 will cause thermalcommunication with multiple sections of the burn portions 532 as the hotwire 544 rotates underneath those sections. The hot wire 544 may rotaterelative to the burn portions 532 because the burn portions 532 arecoupled with the upper portion of the gimbal 500 that can rotaterelative to the bottom portion of the gimbal 500 that includes theseparator assembly 534. The separator assembly 534 may be connected tothe SPB 300 via a shaft or other member so that rotation of the SPB 300relative to the ZPB 200 also rotates the separator assembly 534 relativeto the ZPB 200.

The release assembly 534 thus includes a “burn” type release mechanism.In some embodiments, other release mechanisms may be implemented. Inaddition or alternatively to the burn type release mechanism, therelease assembly 534 may include, for example, cutters that cut therelease lines 526, separation nut mechanisms that separate portions of anut in a nut and bolt assembly, actuated release members that actuateupon command to release the release lines 526, etc. Thus, the particularconfiguration for the release assembly 534 described in detail herein ismerely one example, and many other types of release assemblies 534 maybe implemented with the LTA system 100.

The actuation of the release assembly 534 causes separation of the ZPB200 and the SPB 300. In addition, actuation of the release assembly 534may also cause termination of the flight of the ZPB 200 and/or SPB 300.In some embodiments, termination of the flight of the ZPB 200 isinitiated by “goring.” Goring refers to at least partial removal of atleast one of the gores 225 of the ZPB 200. One or more of the gores 225may be torn from the remaining portions of the skin 220 of the ZPB 200.The gores 225 may be torn from the upper portion 210, for example fromthe top 212, of the ZPB 200.

The gimbal 501 includes the tear line 535. There may be multiple tearlines 535. In some embodiments, the gimbal 501 may not include any tearline 535. The tear line 535 of the gimbal 501 may be similar to the tearline 535 as described above with respect to the gimbal 500. The tearingof gores 225 may be accomplished by the tear line 335. The tear line 535is able to remain attached to the gimbal 501 after actuation of therelease assembly 534. Actuation of the release assembly 534 causes theSPB 300 and portions of the gimbal 501 attached thereto to fall awayfrom ZPB 200. A lower end of the tear line 535 is attached to a lowerportion of the gimbal 501, e.g. to the attachment 529 as shown. An upperend of the tear line 535 on an opposite end may be attached to one ormore of the gores 225 of the ZPB 200 at various locations, for exampleat or near the upper portion 210 of the ZPB 200. The upper end of thetear line 535 may be connected to seams between adjacent gores 225, totape between the gores 225, to the upper ends of the gores 225, to skin220 portions of the gores 225, to other locations, or combinationsthereof. When the SPB 300 with a portion of the gimbal 501 falls awayfrom the ZPB 200, the tear line 535 tears out the corresponding one ormore gores 225 from the ZPB 200, causing destruction of the ZPB 200 andterminating the flight.

In some embodiments, in addition or alternatively to connection with thegimbal 501, the lower end of the one or more tear lines 535 may extendand connect to other components of the LTA system 100. In someembodiments, the tear line 535 may extend from the gores 225 to the SPB300. For example, the release assembly 534 may cause the SPB 300 toseparate from the ZPB 200, and the weight of the now-separated SPB 300may pull on the tear lines, causing the gores 225 to rip away from theZPB 200. In some embodiments, the tear lines extend from the gores 225to the stratocraft 400. For example, the release assembly 534 may causethe SPB 300 to separate from the ZPB 200, and the weight of thenow-separated stratocraft 400 may pull on the tear line 535, causing thegores 225 to rip away from the ZPB 200. By causing the gores 225 to ripaway from the remaining portions of the skin 220 of the ZPB 200, thelift gas inside the ZPB 200 is allowed to escape. The decrease in liftgas causes the ZPB 200 to lose lift, and the weight of the ZPB 200 causea net downward force on the ZPB 200, causing the ZPB 200 to fall to theground.

Various embodiments of the gimbal 501 may include all electricalconnections, wires, controls, etc. routed to and from only the SPB 300side of the gimbal 501. This may allow electrical power and control tocome from the payload support 700 or components thereof. It is also asignificant mass and complexity benefit not to have electricalconnections and wiring routed from both the top and the bottom sides ofthe gimbal 501. For example, with the gimbal 501 electrically connectedon only the SPB 300 side, actuation of the release assembly 534 wouldnot require an electrical disconnect from the ZPB 200 side of the gimbal501, and it would reduce or eliminate the need for any electricalcomponents associated with the gimbal 501 to be in or on the ZPB 200. Insome embodiments, this one-sided arrangement could be reversed such thatall electrical power and control signals, etc. are routed to the ZPB 200side of the gimbal 501. In some embodiments, the various one-sideelectrical configurations may be implemented with the gimbal 500.

The various embodiments of the gimbal, including the gimbal 500 and 501,and the various components thereof, may be electronically controlled. Asfurther described herein, a control system 1000 may electronicallycontrol the gimbal 500 and the various components thereof.

E. Stratocraft

FIGS. 5A and 5B are, respectively, perspective and side views of anembodiment of the stratocraft 400. The stratocraft 400 includes variousfeatures for supporting mission objectives of the system 100, such as apayload and supporting subsystems. The stratocraft 400 includesembodiments of an upper craft 600 and a payload support 700. The uppercraft 600 is coupled with the SPB 300. The upper craft 600 may becoupled with the bottom 317 of the SPB 300. The upper craft 600 may berigidly coupled with the SPB 300. In some embodiments, the connectionbetween the upper craft 600 and the SPB 300 may have the same or similarfeatures and/or functionalities as the various connections between theSPB 300 and the ZPB 200.

The upper craft 600 includes a ladder assembly 610. The ladder assembly610 is an elongated, structural connector that couples the payloadsupport 700 with the SPB 300. The ladder assembly 610 may coupledirectly or indirectly with the SPB 300. The ladder assembly 610 maycouple the payload support 700 with the SPB 300 such that the payloadsupport 700 is located below the SPB 300 when the LTA system 100 is inflight. The ladder assembly 610 may be coupled with the SPB 300 suchthat rotation of the SPB 300 will rotate the ladder assembly 610. Theladder assembly 610 may couple with and/or support other features, asdescribed herein. The ladder assembly 610 includes one or more wires forstructurally supporting the payload support 700, as described in furtherdetail herein, for example with respect to FIG. 5C. The ladder assembly610 also includes an air hose 690, which is a conduit fluidly connectingthe SPB 300 with the compressor assembly 800. In some embodiments, theladder assembly 610 and the air hose 690 are the same components,although they may be separate components, as described herein. Theladder assembly 610 may have a length based at least in part on avoidingshading from the LTA system 100 during daylight, for example in order toprovide sunlight to a solar array 630. Such shading may be due to theSPB 300 and/or ZPB 200 located above the stratocraft 400.

The stratocraft 400 includes the solar array 630. The solar array 630may be part of the upper craft 600, as shown. The solar array 630includes one or more solar panels configured to receive sunlight forconversion to electrical energy. The solar array 630 is generallyplanar. In some embodiments, the solar array 630 may be curved orotherwise flexible. A variety of suitable solar array 630 types may beused, including solar panels with cell efficiencies of about 23%, lowcost per watt, without light-induced degradation, a low temperaturecoefficient, and/or having low light and broad spectral response. Solarpanels of the solar array 630 also include features to address largetemperature variations due to the very hot and very cold extremes of thehigh altitude environment

The solar array 630 is coupled with the ladder assembly 610. The one ormore solar panels of the solar array 630 may be located along the lengthof the ladder assembly 610. The solar array 630 may be directly orindirectly coupled with the ladder assembly 610. The solar array 630 iscoupled with the ladder assembly 610 such that rotation of the ladderassembly 610 will rotate the solar array 630. The solar array 630 may berotated to point at the sun for maximum solar energy conversion, asdescribed herein. The solar array 630 rotates about the longitudinalaxis 105 for azimuth adjustments. In some embodiments, the solar array630 may rotate about multiple axes, for example, for azimuth andelevation adjustments.

The stratocraft 400 includes a bag 640. The bag 640 may be part of theupper craft 600. The bag 640 is used to contain features of a parafoil680, as described herein. The bag 640 may be a parachute bag or similarreceptacle for containing the parafoil 680 features and allowing releasetherefrom. The bag 640 may be formed from a variety of materials,including fabric, other materials, or combinations thereof. The bag 640is coupled with the ladder assembly 610. As shown, the bag 640 isconnected to the ladder assembly 610 by a cord 642. The bag 640 may bedirectly attached to the ladder assembly 610. In some embodiments, thebag 640 may be releasably coupled with the ladder assembly 610.

The stratocraft 400 includes a cover 650. The cover 650 may be part ofthe upper craft 600. The cover 650 is used to contain features of aparafoil 680, as described herein. The cover 650 may be an elongatedtube-like fabric for containing the parafoil 680 features and allowingrelease therefrom. The cover 650 may be formed from a variety ofmaterials, including fabric, other materials, or combinations thereof.The cover 650 is coupled with the bag 640. The cover 650 may be directlyattached to the bag 640. The cover 650 and bag 640 may be part of thesame, continuous sleeve for housing various portions of the parafoil680. For instance, the bag 640 may contain the bunched up canopy portionof the parafoil 680 while the cover 680 contains the lines of theparafoil. The cover 650 has an opening at the lower end for receivingthe parafoil 680 inside the cover 650.

The stratocraft 400 includes the parafoil 680. The parafoil 680 may bepart of the upper craft 600. The parafoil 680 is only partially shown inFIGS. 5A and 5B because it is stowed inside the cover 650 and bag 640.The parafoil 680 may be stowed during flight and then deploy to adeployed flight configuration, as described herein for example withrespect to FIG. 8. The parafoil 680 may be coupled with the ladderassembly 610, for example, via the cover 650 and bag 640.

The parafoil 680 provides a descent system for the payload support 700.The parafoil 680 is initially coupled with the payload support 700 andrestrained during flight. The parafoil 680 is then released from theupper craft 600, for example from the ladder assembly 610, the bag 640and/or the cover 650, at high altitude and controllably descends to alanding site on the ground with the payload support 700. Upon release,the parafoil 680 may slide out of the bag 640 and cover 650 and deployautomatically. Some example embodiments of parafoil technology that maybe used for the parafoil 680 are described, for example, in U.S. patentapplication Ser. No. 15/065,828, filed Mar. 9, 2016, titled RigidizedAssisted Opening System for High Altitude Parafoils, the entiredisclosure of which is incorporated herein by reference for allpurposes.

In some embodiments, the LTA system 100 includes a descent system inaddition or alternative to the parafoil 680. For instance, the LTAsystem 100 may, in addition or alternative to the parafoil 680, includeone or more parachutes, one or more drogue parachutes, otherdecelerators, or combinations thereof. The various descent systems mayhave some or all of the same or similar features and/or functionalitiesas described herein with respect to the parafoil 680. Thus, the variousdescent systems that may be incorporated in the LTA system 100 may haveone or more release mechanisms, etc. In some embodiments, the LTA system100 includes one or more of the descent systems described, for example,in U.S. patent application Ser. No. 14/188,581, filed Feb. 24, 2014, andtitled NEAR-SPACE OPERATIONS, the entire disclosure of which isincorporated by reference herein for al purposes. In some embodiments,the LTA system 100 does not include any descent system.

The stratocraft 400 includes the air hose 690. The air hose 690 may bepart of the upper craft 600 and/or the payload support 700. The air hose690 is a hollow conduit providing for the movement of air therein. Aninner cavity thus extends along at least a portion of the ladderassembly 610 through the air hose 690. In some embodiments, the ladderassembly 610 is hollow from the upper end to the lower end. The air hose690 is formed from a generally flexible material, although in someembodiments it may be partially or entirely rigid. The air hose 690 maybe formed from a variety of suitable materials, including fabrics,fibers, metals, composites, other materials, or combinations thereof.The air hose 690 may be connected to the SPB 300, for example the bottom317, in a variety of suitable manners, including directly attached withfasteners, indirectly attached with brackets, etc. The air hose 690 maybe releasably coupled with the payload support 700, such that release ofthe payload support 700 from the upper craft 600 allows for release ofthe air hose 690 from the payload support 700.

The air hose 690 fluidly connects the SPB 300 with features for airintake and release at or near the payload support 700. Ambient air fromthe surrounding atmosphere may therefore be received at or near thepayload support 700 and transmitted via the air hose 690 to the SPB 300.The air hose 690 may be fluidly coupled with a compressor 810 asdescribed herein, where the compressor 810 is mounted with a payloadsupport 700 and the compressor 810 is fluidly coupled with the interiorvolume of the SPB 300 via the air hose 690. Air from inside the SPB 300may be released through the air hose 690 back to the surroundingatmosphere.

FIG. 5C is a close up view of a portion of the ladder assembly 610. Theladder assembly 610 includes one or more rungs 612. There are two rungs612 visible in the figure. The ladder assembly 610 may include five,ten, twenty, thirty, fifty, one hundred, or other lesser, in between orgreater amounts of rungs 612. The rungs 612 are structural supportslocated along the length of the ladder assembly 610. The rungs 612 maybe generally evenly spaced along the length of the ladder assembly 610from the payload support 700 to the SPB 300.

The rungs 612 include a body 613. The body 613 may be formed from avariety of suitable materials, including metals, composites, plastics,other suitable materials, or combinations thereof. The body 613 may bepartially or entirely rigid, or partially or entirely flexible. The body613 forms a generally triangular shape. In some embodiments, the body613 may form a variety of shapes, including rounded, circular, square,rectangular, other polygonal shapes, other suitable shapes, orcombinations thereof. The body 613 is generally flat.

The body 613 of each rung 612 forms an opening 614 generally though thecenter of the rung 612, The opening 614 is configured, for examplesized, to receive therein the air hose 690. The air hose 690 extendsthrough the series of rungs 612 through the openings 614. The openings614 may be sized to provide for an interference fit with the air hose690. The openings 614 may be sized to provide for a loose with the airhose 690. air hose 690 extends along the length of the ladder assembly610. The ladder assembly 610 may at least partially support the air hose690, for example via the rungs 612. In some embodiments, the air hose690 is supported at various locations along the ladder assembly 610 bythe rungs 612. In some embodiments, the air hose 690 may extendpartially or completely along the outside of the ladder assembly 610.

The rungs 612 include one or more guide openings 616. As shown, eachrung 612 includes three guide openings 616. The guide openings 616 arelocated at or near the edges of the body 613. As shown, the guideopenings 616 are located at the vertices of the triangular-shaped rungs612. The guide openings 616 define spaces configured to receive thereina ladder rope 620.

The ladder assembly 610 includes one or more ladder ropes 620. As shownin FIG. 5C, the ladder assembly 610 includes three ladder ropes 620. Insome embodiments, the ladder assembly 610 may include less than or morethan three ladder ropes 620. The ladder ropes 620 are structuralconnectors that connect the payload support 700 with the SPB 300. Theladder ropes 620 may be formed from a variety of suitable materials,including composites, fibers, metals, plastics, other suitablematerials, or combinations thereof. The ladder ropes 620 may secure therungs 612 in place. For example, clips, knots, or other features of theladder ropes 620 may be incorporated at desired spacings to secure therungs 612 at corresponding desired spacings. The ladder ropes 620 may bereleasably connected with the payload support 700, as described herein.The ladder ropes 620 may couple with the SPB 300 directly or indirectly,for example via structural connectors located at the bottom 317 of theSPB 300, or otherwise with the lower portion of the SPB 300. In someembodiments, the ladder ropes 620 may extend all the way to the ZPB 200,for example for connection to the top of the gores 225 for goring theZPB 200 upon flight termination, as described herein.

The rungs 612 may couple other features with the ladder assembly 610.The rungs 612 may connect the solar array 630, the cord 642, the bag640, the cover 650, the parafoil 680, and/or other features with theladder assembly 610.

F. Payload Support

FIG. 6 is a top perspective view of an embodiment of the payload support700. The payload support 700 provides structural support to a payload730 and other subsystems. The payload 730 may be a variety of differentsystems, including but not limited to instruments and passenger spacecapsules, as further described herein. Thus, while the particularembodiment shown is related to a particular payload 730 and payloadsupport 700 with particular configurations, the disclosure is notlimited to only these features and configurations. A variety of otherpayloads and support structures and configurations may be used with thesystem 100. For reference, a direction P is indicated. The direction Pis a geometric reference direction that is “fixed” to the payloadsupport 700 frame of reference, such that the direction P points indifferent directions as the payload support 700 rotates.

The payload support 700 includes a frame 710. The frame 710 is a rigidstructure providing support and stability to various features of thesystem 100. The frame 100 may be formed from a variety of suitablematerials, including metals, composites, other materials, orcombinations thereof. The frame 710 may have a variety ofconfigurations. As shown, the frame 710 is in the shape of atetrahedron. The frame 710 thus has three side faces 711, 712, 713. Onlyside faces 711 and 712 are visible in FIG. 6, with side face 713 locatedon the backside of the payload support 700 as oriented in the figure. Alower face 714 is located on the lower end of the payload support 700and partially in between the three side faces 711, 712, 713. The lowerface 714 may be entirely or substantially open. The lower face 714 mayinclude the payload 730, as described herein. The faces 711, 712, 713may be planar as shown, or have other contours, and be located generallyin between side members of the frame 710. The tetrahedral frame 710forms an apex at the intersection of the frame 710 members that pointsin the direction P, which is away from the lower face 714. As shown, thedirection P may align with the +Z direction. In some embodiments, thedirection P may not align with the +Z direction.

The payload support 700 is releasably coupled with the upper craft 600.The payload support 700 is attached during flight to the upper craft600, such as to the ladder ropes 620. The payload support 700 is thenreleased for descent back to ground with the parafoil 680 and payload730.

The payload support 700 is coupled with the upper craft 600 via aflaring bracket 715, parafoil lines 682, and release lines 719. Upperends of the release lines 719 are attached to the upper craft 600 andlower ends of the release lines 719 are releasably attached to thepayload support 700. Upon release of the lower ends of the release lines719 from the payload support 700, an increased downward force is thenapplied to the flaring bracket 715, due to the loss of support from therelease lines 719, ultimately causing the flaring bracket 715 toseparate from the payload support 700 and re-orient the payload support700.

In some embodiments, the increased force due to release of the releaselines 719 causes the payload support 700 along with the attachedparafoil 680 to fall from the upper craft 600. The parafoil 680 thusslides out of the cover 650 and bag 640. After the parafoil 680 exitsthe cover 650 and bag 640, the parafoil 680 deploys into flightconfiguration. Upon deploying into flight configuration, a force due todeceleration is transmitted to the flaring bracket 715. The flaringbracket 715 is held down by a cord that breaks at a threshold force. Theforce due to deceleration exceeds this threshold force and breaks thecord, causing the flaring bracket 715 to separate from the payloadsupport 700. The detachment or separation of the flaring bracket 715thus causes the payload support 700 to re-orient, as described below.

In some embodiments, the increased force due to release of the releaselines 719 alone causes the flaring bracket 715 to release. In this case,the flaring bracket 715 has separated before the payload support 700 hassignificantly fallen from the upper craft 600 and before the parafoil682 has slid out of the cover 650. The flaring bracket 715 thusseparates from the frame 710 as the payload support 700 falls away fromthe upper craft 600. As the payload support 700 falls away, the parafoil680, which is attached to the payload support 700 via the parafoil lines682, is pulled out of the cover 650 and bag 640. After the parafoil 680exits the cover 650 and bag 640, the parafoil 680 deploys into flightconfiguration. Further, the parafoil lines 682 are attached at locationsof the payload support 700 such that the payload support 700 re-orientsupon release of the flaring bracket 715, as described below.

Lower ends of the parafoil lines 682 are connected at locations of theframe 710 such that the payload support 700 re-orients, e.g. rotates,upon release from the upper craft 600. In some embodiments, the parafoillines 682 are connected with the lower face 714, such as with asupporting bracket of the lower face 714. As shown, the flaring bracket715 is coupled with lines 682 of the parafoil 680. The release lines 719also releasably couple the payload support 700 with the upper craft 600.As shown, three release lines 719 extend through a guide 717 and upalong the ladder assembly 610. The release lines 719 may be releasedfrom the payload support 700.

The payload support 700 includes landing pads 721, 722, 723. The landingpads 721, 722, 723 are structural absorbers configured to absorb impactupon landing. As shown, there are three landing pads 721, 722, 723located in corners of the first side face 712. In some embodiments,there may be less than or greater than three landing pads and/or in avariety of locations. The landing pads 721, 722, 723 may be crushablestructures that collapse upon landing to attenuate forces due tolanding, for example to protect the payload and other systems. Thepayload support 700 also includes bumpers 726, 727 on a frame 710 memberlocated opposite the side face 712 and the landing pads 721, 722, 723.The bumpers 726, 727 provide extra protection for the frame 710, forexample in the event of rollover upon landing.

The payload support 700 includes the payload 730. The payload 730 iscoupled with the payload support 700, for example structurally attached.The payload 730 may be coupled with the payload support 700 so that itis dynamically and/or vibrationally isolated from the payload support700 to attenuate force transmission from the payload support 700 to thepayload 730. The payload 730 is located generally at or near the lowerface 714 of the payload support 700. The payload 730 may therefore befacing toward ground while the system 100 is in flight. The payload 730may be considered “nadir-pointing,” for example the payload 730 may havea field of view that points generally toward the ground. The payload 730may be or have a variety of suitable systems, sensors, computingcapabilities, etc. In some embodiments, the payload 730 is aninstrument, for example an optical instrument. In some embodiments, thepayload 730 is a sensor or sensor suite, for example infrared, visual orthermal sensors. The payload 730 may be other types of systems, orcombinations thereof. The payload 730 may weigh about 200 pounds.Depending on the embodiments, the payload 730 may be within a range ofweights from about 30 pounds or less to about 500 pounds or more.

The LTA system 100 includes one or more sensors 740. As shown, thepayload support 700 includes one or more sensors 740. The sensors 740are coupled with the frame 710. The sensors 740 may be in a variety ofdifferent locations of the payload support 700. The sensors 740 may belocated or otherwise associated with the payload 730, a compressorassembly 800, and/or other subsystems or components of the payloadsupport 700.

The sensors 740 are devices for detecting various parameters andproviding a corresponding output indicative of those parameters. Thesensors 740 may be coupled with the LTA system 100 and configured todetect an environmental parameter or attribute. The parameters detectedmay be related to various events, changes, properties, etc. Suchparameters may be related to the LTA system 100 or components thereof,and/or to the surrounding environment (e.g. atmosphere). The sensors 740may be a variety of different types of sensors. The sensors 740 may bepressure sensors (such as transducers) for detecting the ambientpressure, which may be used for, among other things, determiningaltitude. The sensors 740 may be temperature sensors for detectingambient temperature, which may be used for among other things,determining air flow rates or intended pressures for the SPB 300. Thesensors 740 may be accelerometers and/or gyroscopes, which may be usedfor among other things determining position, velocity and accelerationof the LTA system 100 or various components thereof. The sensors 740 maybe sun sensors, which may be used for among other things pointing thesolar array 630 toward the sun. These are just some examples, and thesensors 740 may be many other different types of sensors and based onmany other sensing principles, including light sensors, infraredsensors, thermocouples, potentiometers, magnetic field sensors,gravitational sensors, humidity sensors, moisture sensors, vibrationsensors, electrical field sensors, sound sensors, forces sensors, straingages, piezoelectric sensors, resistive sensors,micro-electro-mechanical sensors (MEMS), ultrasonic sensors, humiditysensors, gas sensors, chemical sensors, flow sensors, other sensors, orcombinations thereof.

Besides the payload support 700, the sensors 740 may in addition oralternatively be included with various other components of the LTAsystem 100, for example with the ZPB 200, the SPB 300, the gimbal 500,the upper craft 600, the solar array 630, the parafoil 680, the payload730, the various release mechanisms, other features of the system 100,or combinations thereof. In some embodiments, one or more sensors 740are located or otherwise associated with the ZPB 200 and/or the SPB 300.For example, the ZPB 200 and/or the SPB 300 may include pressure sensorsfor detecting internal pressures, flow sensors for detecting the flow ofair into and/or out of the balloons, temperature sensors for detectingthe temperature inside and/or outside of the balloons or of the balloonmaterials, accelerometers and/or gyroscopes for detecting theacceleration and/or velocity of the balloons, position sensors fordetecting the positions of the balloons or of various components orportions of the balloons, etc.

The payload support 700 includes a compressor assembly 800. Thecompressor assembly 800 is coupled with the payload support 700. Thecompressor assembly 800 is shown mounted within the payload support 700.The compressor assembly 800 may be coupled with the payload support in avariety of suitable ways, including indirectly attached via brackets orother structures, directly attached to the frame 710, other suitableattachment means, or combinations thereof. The compressor assembly 800provides for moving ambient air from the surrounding atmosphere into theSPB 300, and for moving air contained inside the SPB 300 back to thesurrounding atmosphere, as described herein. The compressor assembly 800is therefore fluidly coupled with ambient air in the surroundingatmosphere and fluidly coupled with the interior of the SPB 300. Thecompressor assembly 800 is coupled with the SPB 300 via the air hose690. As shown, the air hose 690 extends upward from the compressorassembly 800 and through the ladder assembly 610. This is merely one ofa number of suitable configurations. For instance, the air hose 690 mayextend in different directions from the compressor assembly 800, mayextend along the outside of the ladder assembly 610, etc.

G. Compressor and Valve

FIGS. 7A and 7B are perspective views of the compressor assembly 800.For clarity, the compressor assembly 800 in FIGS. 7A and 7B is shown inisolation from other features of the LTA system 100. The air hose 690and payload support 700, among other features, are therefore not shownin FIGS. 7A and 7B. FIG. 7A shows a first side perspective view of thecompressor assembly 800, and FIG. 7B shows an opposite side perspectiveview of the compressor assembly 800.

The compressor assembly 800 causes ambient air from the surroundingatmosphere to enter the compressor assembly 800. The ambient airentering the compressor assembly 800 flows into the compressor assembly800 generally in the direction 801. Air inside the compressor assembly800 can flow out of the compressor assembly 800 and generally in thedirection 802. The air flowing out of the compressor assembly 800 in thedirection 802 flows toward the SPB 300 to provide more air inside theSPB 300. Air from inside the SPB 300 can flow back into the compressorassembly 800 in the general direction 803 to provide less air inside theSPB 300. Air from inside the compressor assembly 800 can also flow outof the compressor assembly 800 in the general direction 804 and/or 805.The air flowing out of the compressor assembly 800 in the directions 804and 805 flows back into the surrounding atmosphere, for example to ventair from the SPB 300. The compressor assembly 800 is controllable tocause the air to flow in the directions 801, 802, 803, 804, 805 asdescribed herein. It is understood that the directions 801, 802, 803,804, 805 are illustrative only, and that the air may flow alongdifferent flow lines that are still generally in the directions 801,802, 803, 804, 805.

The compressor assembly 800 includes a compressor 810. The compressor810 causes ambient air from the surrounding atmosphere to enter thecompressor assembly 800. The compressor 810 is in fluid communicationwith the ambient air and with the interior volume of the SPB 300 and isconfigured to compress the ambient air and pump the compressed air intothe interior volume of the SPB 300 to increase the downward force to theLTA system 100. The increased downward force to the LTA system 100 isdue to compressing the air internal to the SPB 300, thus making thecompressed air density greater than the surrounding ambient air.

The compressor 810 is a mechanical device that increases the pressure ofthe air taken in from the surrounding atmosphere and transports ittoward the SPB 300. The particular compressor 810 type may depend on theparticular mission. For higher altitude and/or heavy payload liftingmissions, the compressor 810 is a centrifugal compressor, that mayinclude an inlet, impeller, diffuser, and collector.

The centrifugal version of the compressor 810 uses a rotating impellerto force the ambient air to the impeller, thus increasing the velocityof the gas. The diffuser then converts the velocity energy to pressureenergy. The centrifugal version of the compressor 810 may includemultiple stages. In some embodiments, the compressor 810 is a two stage,centrifugal compressor, which is improved or optimal for higher pressureratios at high altitude and/or for heavy payload lifting missions. Thetwo stage, centrifugal version of the compressor 810 may produce about4000 watts (W) or about 6 horsepower (hp), have a compression ratio ofgreater than about 3:1, and/or achieve differential pressures of about0.5 pounds per square inch (PSI). In some embodiments, the centrifugalversion of the compressor 810 comprises two or more stages, and isconfigured to provide at least 500 liters of the ambient air per secondto the interior volume of the SPB at altitudes above 50,000 feet, aboveabout 70,000 feet, and/or other high altitudes. The centrifugalcompressor may be configured to provide the ambient air to the interiorvolume of the SPB 300 such that a resulting descent rate of the LTAsystem 100 is at least 10,000 feet per hour at altitudes above about50,000 feet, above about 70,000 feet, and/or other high altitudes. Theresulting descent rate of the LTA system 100 may be at least 20,000 feetper hour at altitudes above about 50,000 feet, above about 70,000 feet,and/or other high altitudes. The compressor 810 may provide a flow rateof about 500 liters per second (lps) at altitudes above about 50,000feet, above about 70,000 feet, and/or other high altitudes. Depending onthe embodiment, the compressor 810 may provide a flow rate within arange of flow rates from about 350 lps or less to about 1000 lps or moreat altitudes above about 50,000 feet, above about 70,000 feet, and/orother high altitudes.

The compressor assembly 800 includes an air intake 812. The air intake812 provides a structural feature through which the ambient air in thesurrounding atmosphere enters the compressor assembly 800. The airintake 812 is designed to provide for high flow rate of air, dependingon the required air intake of the LTA system 100. The air intake 812defines an opening 813. The air entering the air intake 812 flowsthrough the opening 813, in the general direction 801. The air enteringthe opening 813 of the air intake 812 may flow from an envelope 814. Asshown, the envelope 814 is conical. The conical shape of the envelop 814ensures laminar flow through the air intake 812 and to the impeller. Insome embodiments, the envelope 814 may have other shapes. The envelope814 is generally free of obstructions to allow for generallyunobstructed air flow into the opening 813 of the air intake 812. Asshown, the opening 813 is a circular space defined by the air intake812. In some embodiments, the opening 813 may have other suitableshapes. The opening 813 may be an open space largely free of otherstructures. In some embodiments, the opening 813 and/or air intake 812may include filters, vents, channels, other structures, or combinationsthereof.

The compressor assembly includes a volute 816 fluidly coupled with theopening 813. The volute 816 provides a conduit through which ambient airthat enters the opening 813 is transported to other locations. Thevolute 816 is a conduit through which the impeller of the compressor 810delivers the compressed air to the rest of the compressor assembly 800.The volute 816 may include the impeller therein.

The compressor assembly 800 includes a mount 820. The mount 820 supportsthe compressor assembly 800. The mount 820 is coupled with the payloadsupport 700. The mount 820 may be directly or indirectly attached to thepayload support 700. As shown, the compressor assembly 800 includesmultiple springs 822. The springs 822 couple the mount 820 with thepayload support 700, either directly or indirectly. The springs 822 areelastic structures, and may be coil springs, extension springs,compressive springs, other suitable springs, or combinations thereof.The mount 820 and springs 822 structurally (e.g. dynamically,vibrationally, etc.) isolate the compressor 810 from the payload support700, and vice versa. Vibrations and other movements of the compressorassembly 800, for instance due to the rotational velocity of theimpeller of the compressor 810, are attenuated so that such disturbancesare not entirely transmitted to the payload support 700. For example,vibrations due to operation of the compressor 810 are attenuated tomitigate or prevent disturbances from such vibrations affecting theoperation of the payload 730, such as an optical instrument. Thecompressor 810 is electrically connected to a speed controller via anelectrical connection 824. The electrical connection 824 is inelectrical communication with the control system 100 for control of thecompressor 810. The compressor assembly 800 also includes an outlet 826.The outlet 826 couples the volute 816 with a manifold 850. The outlet826 is configured to couple the volute 816 of the compressor 810 to theair manifold 850.

The compressor assembly 800 includes the manifold 850. The manifold 850is a structural channel providing for air flow through the manifold 850.The manifold 850 fluidly coupled various features of the compressorassembly 800. The manifold 850 is fluidly coupled with the compressor810 via the volute 816 and outlet 826. The manifold 850 is also fluidlycoupled with the SPB 300 and the surrounding atmosphere. The manifold850 thus provides for air movement between the compressor 810, the SPB300 and the surrounding atmosphere. For example, air may flow from thecompressor 810 and into the manifold 850 and then from the manifold 850and into the SPB 300. As further example, air may flow from the SPB 300and into the manifold 850 and then from the manifold 850 and into thesurrounding atmosphere. The air inside the manifold 850 may flow intothe surrounding atmosphere via a controlled valve 870 and/or emergencyvalve 871, as described herein. In some embodiments, the air inside themanifold 850 may flow into the surrounding atmosphere back through thecompressor 810. For example, the compressor 810 may allow for reversibleair flow. In some embodiments, the compressor 810 may passively allowfor reversible air flow. In some embodiments, the compressor 810 mayactively allow for reversible air flow, for example by actively causingair to exit the compressor 810, which may be out through the opening 813of the intake 812.

The compressor assembly 800 includes a hose coupling 852 having anopening 854. The hose coupling 852 may define the opening 854. The hosecoupling 852 provides for a fluid connection through the opening 854with the SPB 300, which may be via the air hose 690. The hose coupling852 may therefore couple with the air hose 690 to allow for air flowfrom the manifold 850, through the opening 854, through the air hose 690and into the SPB 300. The compressor 810 causes the air to enter themanifold 850 and flow through the air hose 690 to pressurize the SPB300.

The compressor assembly 800 includes the controllable valve 870, as bestseen in FIG. 7B. The valve 870 is a device for controllably allowing airflow from the compressor assembly 800. In some embodiments, thecompressor assembly 800 may include two valves: the controllable valve870 that is actively controllable to achieve the desired vent rate ofair from the SPB 300, and the emergency valve 871 being a passiveemergency pressure relief valve designed to prevent the SPB 300 frombeing over pressurized thus protecting the SPB 300.

The controllable valve 870 regulates, directs or controls the flow ofair by opening, closing, or partially obstructing various passageways.The air from inside the SPB 300 is fluidly connected to the manifold 850such that opening the valve 870 allows for air to flow from the SPB 300and into the surrounding atmosphere due to a higher pressure inside theSPB 300 relative to the surrounding atmosphere. In some embodiments, thevalve 870 is adjustable, in fluid communication with the ambient air andwith the interior volume of the SPB 300, and is configured to beadjusted to release the pumped-in ambient air from the interior volumeof the SPB 300 to the surrounding atmosphere to decrease the downwardforce to the LTA system 100. In some embodiments, the valve 870 isadjustable and is configured to be adjusted to release the pumped-inambient air from the interior volume of the SPB 300 to the surroundingatmosphere such that a resulting ascent rate of the LTA system 100 is atleast 10,000 feet per hour at altitudes above about 50,000 feet, aboveabout 70,000 feet, and/or other high altitudes. The resulting ascentrate of the balloon system may be at least 20,000 feet per hour ataltitudes above about 50,000 feet, above about 70,000 feet, and/or otherhigh altitudes.

As shown, the valve 870 includes a plate 875 that can be selectivelymoved to create an opening 877. The opening 877 is a passageway thatfluidly connects the manifold 850 with the surrounding atmosphere. Aircan thus flow from the manifold 850 and through the opening 877 into thesurrounding atmosphere. The air flow may be passive such that air willflow from the manifold 850 and into the surrounding atmosphere when thepressure of the air inside the manifold 850 is greater than the pressurein the surrounding atmosphere. In some embodiments, the valve 870 may bepassive, active or combinations thereof. The valve 870 may be one-way,such that air may only flow in one direction through the valve 870. Insome embodiments, the valve 870 may only allow for air flow from insidethe manifold 850 and into the surrounding atmosphere, which may be inthe general direction 805. The plate 875 can be moved to close the valve870 and thus seal the opening 877 to prevent air flow through the valve870.

The plate 875 is moved by an actuator 879 via a rod 880. The actuator879 can actuate, e.g. rotate, translate, preform other movements, orpreform combinations thereof, to move the rod 880 and thus the plate875. The actuator 879 is controllably actuated via electricalcommunication from the control system 1000 and/or from a ground stationor satellite. The actuator 879 may cause the plate 875 to move bepredetermined amounts. The actuator 879 may cause the plate 875 to moveby various amounts to control the venting rate of air. In someembodiments, the valve 870 includes an air flow rate sensor such thatmovement of the plate 875 via the actuator is controlled based on adesired air flow rate. The actuator or portions thereof may be coupledwith and/or enclosed in a housing 882. The housing 882 is supported byfour supports 884. The supports 884 are connected to the manifold 850.

This is one of many suitable configurations of the valve 870, and othersuitable configurations may be implemented that allow for selectiveopening and closing of the valve 870. Further, the valve 870 may be orinclude a number of types of valves, components, other devices,structures, mechanisms, etc., for preventing and allowing air flow,including but not limited to vents, hydraulic valves, pneumatic valves,manual valves, solenoid valves, motors, bonnets, plugs, balls, ports,handles, actuators, discs, seats, stems, gaskets, springs, trims, orcombinations thereof. In some embodiments, there may be more than onecontrollable valve 870. In some embodiments, the valve 870 may be partof the compressor 810, for instance where the compressor 810 allows forair flow into the surrounding atmosphere.

The valve 870 allows for air to flow from the SPB 300 and into thesurrounding atmosphere. Air from the SPB 300 is in fluid connection withthe manifold 850 such that opening the valve causes air to flow from theSPB 300, through the manifold 850, and through the valve 870 into thesurrounding atmosphere. The rate of air flow out of the SPB 300 may becontrolled by controlling the valve 870. The control of the air flowrate though the valve 870 may be passive such that controllably openingthe valve 870 determines the air flow rate out of the SPB 300. Forexample, the valve 870 may be completely opened for maximum air flowrate out of the SPB 300. The valve 870 may be partially opened for lessthan maximum air flow rate out of the SPB 300. The valve 870 mayactively control air flow, for example with a fan, such thatcontrollably actuating the valve 870, for example controllably actuatingthe fan, actively controls the air flow rate out of the SPB 300.

The compressor assembly 800 includes the emergency valve 871. The valve871 is an emergency pressure relief valve for allowing air flow from thecompressor assembly 800, for example in the event of an overpressurization of the SPB 300. The valve 871 regulates, directs orcontrols the flow of air by opening, closing, or partially obstructingvarious passageways. In some embodiments, the valve 871 is adjustable,in fluid communication with the ambient air and with the interior volumeof the SPB 300, and is configured to be automatically adjusted torelease the pumped-in ambient air from the interior volume of the SPB300 if internal pressures are too high.

As shown, the valve 871 includes a plug 876 that can be selectivelymoved to create an opening 878. The opening 878 is a passageway thatfluidly connects the manifold 850 with the surrounding atmosphere. Aircan thus flow from the manifold 850 and through the opening 878 into thesurrounding atmosphere. The air flow may be passive such that air willflow from the manifold 850 and into the surrounding atmosphere when thepressure of the air inside the manifold 850 is greater than the pressurein the surrounding atmosphere. In some embodiments, the valve 871 may bepassive, active or combinations thereof. The valve 871 may be one-way,such that air may only flow in one direction through the valve 871. Insome embodiments, the valve 871 may only allow for air flow from insidethe manifold 850 and into the surrounding atmosphere, which may be inthe general direction 805. The plug 876 can be moved to close the valve871 and thus seal the opening 878 to prevent air flow through the valve871. This is one of many suitable configurations of the valve 871, andother suitable configurations may be implemented such as those describedwith respect to the controllable valve 870.

The valve 871 allows for air to flow from the SPB 300 and into thesurrounding atmosphere automatically when pressures inside the SPB 300are too high. Air from the SPB 300 is in fluid connection with themanifold 850 such that opening the valve causes air to flow from the SPB300, through the manifold 850, and through the valve 871 into thesurrounding atmosphere. The valve 871 may be in electrical communicationwith a sensor via the control system 100. For example, a sensor insidethe SPB 300 may detect an internal pressure of air inside the SPB 300and if this pressure satisfies a pressure threshold then the controlsystem 1000 may trigger the valve 871 to open. In some embodiments, insuch situations the controllable valve 870 may also be triggered toopen, for example where the vent rate of the emergency valve 871 isinadequate for a given internal pressure of the SPB 300. In someembodiments, the emergency valve 871 may be used in lieu of thecontrollable valve 870 for descent, for example where the controllablevalve 870 is malfunctioning or otherwise not providing the desireddescent rate. In some embodiments, the emergency valve 871 may be usedin addition to the controllable valve 870, for example where a fastervent and descent rate is desired than is obtainable with only thecontrollable valve 870. Further, there may be more than one emergencyvalve 871.

The payload support 700 may further include a variety of subsystems tosupport the mission. In some embodiments, the payload support 700 mayinclude communications, electrical, power, thermal, avionics, telemetry,guidance navigation and control (GNC), release, termination, and/orother subsystems, or combinations thereof.

The payload support 700 and the various components and subsystemsthereof may be electronically controlled. As further described herein,the control system 1000 may electronically control the payload support700 and the various components thereof, such as the compressor assembly800, the payload 730, the parafoil 680, the various release mechanisms,the various subsystems, etc. The control system 1000 may electronicallycontrol the compressor assembly 800 and the various components thereof.As further described herein, in some embodiments, the compressor 810 iscontrolled for controllably providing air to the SPB 300, for example todescend in altitude or to maintain an altitude. In some embodiments, thecompressor 810 is controlled for controllably releasing air from the SPB300, for example to ascend in altitude or to maintain an altitude.

H. Descent System

FIG. 8 is a perspective view of the parafoil 680. The parafoil 680 isshown separated from the LTA system 100 and in a deployed flightconfiguration with the payload support 700. As described herein, theparafoil 680 separates from the upper craft 600 and deploys in theflight configuration to descend to ground with the payload support 700.In some embodiments, the parafoil 680 may be configured to deploy intothe flight configuration before separating from the rest of the LTAsystem 100. Thus, the descriptions of particular configurations of theparafoil 680, and of particular deployment and flight procedures of theparafoil 680, are not meant to limit the scope of the LTA system 100 andrelated methods to only those particular configurations and procedures.

The parafoil 680 includes a canopy 684. The canopy 684 is shown in thedeployed, flight configuration. The canopy 684 is at least partially asoft structure that provides lift to the parafoil 680. The canopy 684may have more rigid features, such as stiffeners, local attachments,etc. The deployed canopy 684 is generally shaped like a bent wing, witha cross-sectional geometry approximating an airfoil shape. The canopy684 may have openings allowing for air to flow through and into thecanopy 684. Such air flow may assist with achieving and/or maintainingthe deployed shape of the canopy 684. The canopy 684 is capable of beingstowed in a collapsed configuration and of deploying into the flightconfiguration. The stowed canopy 684 is stored within the bag 640 and/orwithin the cover 650 of the stratocraft 400. As discussed, the parafoil680 may be released from the upper craft 600, for example from the bag640 and/or cover 650. The canopy 684 may be released from the bag 640and/or cover 650 upon deployment of the parafoil 680.

The parafoil 680 includes one or more lines 682. The lines 682 couplethe canopy 684 with the payload support 700. As shown, there aremultiple lines 682 attaching the canopy 684 to the flaring bracket 715of the payload support 700. The flaring bracket 715 is shown in adetached configuration, where the flaring bracket 715 has detached fromthe payload support 700. The lines 682 may couple the flaring bracket715 to various locations of the canopy 684, including the front, back,center, one or more sides, other locations, or combinations thereof, ofthe canopy 684. The lines 682 transmit a lifting force from the canopy684 to the payload support 700. The lines 682 may be formed of a varietyof suitable materials, including fiber, composite, metallic, othermaterials, or combinations thereof.

The lines 682 may be rigid or rigidized to assist with the deploymentprocess of the parafoil 680. The lines 682 may extend through a rigidsleeve such as a composite tube, or have a rigid rod inserted into themin order to prevent entanglement during deployment and to assist in theopening of the canopy 684 at high altitudes where air densities are low.In some embodiments, some or all of the lines 682 may be rigidized. Forexample, some of the lines 682 may include relatively stiffer coversaround the lines. Such stiff covers of the lines 682 may assist withdeployment of the lines 682 and/or with mitigating or preventingentanglement of the lines 682. In some embodiments, the parafoil 680includes one or more rigidized assist opening members. For example, theparafoil 680 may include flexible rods that connect the payload support700 to the canopy 684. The flexible rods may store potential energy in aflexed, stowed state and use that energy to assist with releasing anddeploying the canopy 684 into flight configuration. Such flexible rodsmay be in addition or alternatively to the stiffened lines 682. Theseare merely some examples of the multitude of configurations for parafoil680. Further details of some of these and other configurations for theparafoil 680 are described, for example, in U.S. patent application Ser.No. 15/065,828, filed Mar. 9, 2016, titled Rigidized Assisted OpeningSystem for High Altitude Parafoils, the entire disclosure of which isincorporated herein by reference for all purposes.

The parafoil 680 is shown in flight attached to the payload support 700.As mentioned, the LTA system 100 may re-orient the payload support 700in flight relative to its orientation when coupled with the upper craft600. The payload support 700 is thus shown in FIG. 8 re-orientedrelative to the orientation shown in FIG. 6. In particular, in FIG. 8the direction P is now at an angle with respect to the +Z direction. Thepayload support 700 has thus rotated about ninety degrees. The lowerface 714 is no longer facing in the −Z direction. The side face 712 isnow facing generally in the −Z direction. By not facing the lower face714 in the −Z direction, the payload 730 which is generally locatedalong the lower face 714 is further protected for landing. For instance,the payload support 700 will land on the −Z pointing side face 712 andnot on the side-facing lower face 714. Thus, the lower face 714 can beused to point the payload 730 toward ground during flight but thenrotate to land on a different face and protect the payload 730. Further,the landing pads 721, 722, 723 are now facing in the −Z direction andcan thus absorb most or all of the impact upon landing. In addition, thebumpers 726, 727 provide for further protection, for example if thepayload support 700 rolls over forward upon landing. The side face 713is on the back of the payload support 700 as oriented, and is thus notvisible. This is merely one example of the orientation that the payloadsupport 700 may assume after being re-oriented, and other orientationsmay be implemented.

The payload support 700 may re-orient using one or more line extensions750. The line extensions 750 are extensions of the parafoil lines 682.Some or all of the line extensions 750 may be separate lines coupledwith the flaring bracket 715 and/or with the parafoil lines 682. Some orall of the line extensions 750 and corresponding parafoil lines 682 maybe part of one, continuous line. The line extensions 750 are attached tothe payload support 700 in particular locations to cause the payloadsupport 700 to re-orient upon release from the upper craft 600. Asshown, the line extensions 750 are coupled with frame 710, for examplenear the bumper 727, and generally in the P direction. Other lineextensions 750 are coupled with the lower face 714, for example with thepayload 730 or other components. The flaring bracket 715 is locatedgenerally above the bumper 726.

I. Other LTA System Configurations

FIGS. 9A-9E depict alternate embodiments of the LTA system 100. FIGS. 9Aand 9B are side views of another embodiment of an LTA system 101. TheLTA system 101 may have some of the same or similar features and/orfunctionalities as the LTA system 100, and vice versa. The LTA system101 shown in FIG. 9A is at a different point in time than the LTA system101 shown in FIG. 9B.

The LTA system 101 is shown in flight. The LTA system 101 includes theZPB 200 coupled in tandem above the SPB 300. The LTA system 101 has anunderinflated ZPB 200 and SPB 300 in FIG. 9A relative to FIG. 9B. By“underinflated” it is meant the ZPB 200 and SPB 300 are not inflated ator near maximum capacity. The ZPB 200 and SPB 300 are inflated more inFIG. 9B relative to FIG. 9A. Thus, the ZPB 200 and SPB 300 arerelatively contracted in FIG. 9A and relatively expanded in FIG. 9B. TheLTA system 101 may have the configuration shown in FIG. 9A duringtakeoff or at relatively lower altitudes. The LTA system 101 may havethe configuration shown in FIG. 9B at relatively higher altitudes. Thus,the ZPB 200 and SPB 300 may expand as the LTA system 101 climbs inaltitude. For example, the ZPB 200 may expand as the LTA system 101reaches altitude with lower ambient air pressure, such that the LTA gasinside the ZPB 200 causes the ZPB 200 to expand. As further example, theSPB 300 may have insufficient air inside to pressurize it, such that theSPB 300 expands as more air flows into the SPB 300 and contracts as airis released from the SPB 300. As further example, the ZPB 200 may loseLTA gas at high altitudes where the ZPB 200 has reached maximum volumeand cannot expand any further but with rising temperatures causing theinside LTA gas to expand, thus causing trapped air and/or LTA gas toexit the ZPB 200, such as through one or more openings in the ZPB 200.These and other effects, or combinations thereof, may cause the varyingconfigurations (shapes, sizes, etc.) of the ZPB 200 and SPB 300.

The LTA system 101 includes the payload support 700 coupled below theSPB 300. The LTA system 101 does not include an elongated connection,such as the ladder assembly 610, between the payload support 700 and theSPB 300. Thus, in some embodiments, the payload support 700 may belocated closer to the SPB 30. The payload support 700 may be coupleddirectly underneath the SPB 300.

The LTA system 101 includes the compressor assembly 800. The compressorassembly 800 may be mounted with the payload support 700, as describedherein. Thus, the compressor assembly 800 may be located closer to theSPB 300. The compressor assembly 800 may be coupled directly underneaththe SPB 300. Further, the compressor assembly 800 need not be part ofthe payload support 700. In some embodiments, the compressor assembly800 may be separate from the payload support 700. In some embodiments,the compressor assembly 800 is directly coupled with the SPB 300 and avariety of different payload supports 700 may be separately incorporatedwith the LTA system 101. This may allow, for example, a modular LTAsystem 100 or 101 having the advanced maneuver and mission capabilitiesdescribed herein but that can also be used with a variety of differentpayloads and payload supports. For instance, the compressor assembly 800may be coupled directly underneath the SPB 300 and be configured for avariety of different payload supports to be coupled underneath thecompressor assembly 800. These are merely some examples, and othersuitable configurations may be implemented.

Other embodiments of the LTA system 100 besides those described hereinmay be implemented without departing from the scope of this disclosure.In some embodiments, the LTA system 100 may include instruments, thecompressor assembly 800, the parafoil 680, other descent systems besidesthe parafoil 680, additional payloads 730 and/or payload supports 700,an additional ballast hopper, and/or other systems, located above theSPB 300 and below the ZPB 200. Some exemplary configurations of suchsystems are described, for example, in U.S. provisional patentapplication No. 62/294,189, entitled VARIABLE ALTITUDE AIR BALLASTBALLOON SYSTEM and filed Feb. 11, 2016, the entire disclosure of whichis incorporated by reference herein for all purposes.

FIGS. 9C, 9D and 9E depict other embodiments of the LTA systems 100including, respectively, LTA systems 102, 103 and 104, having multipleSPB's 300 and/or a single SPB 300 having multiple, SPB-shaped internalair compartments. Thus, the description of “multiple SPB's” is not meantto exclude the configuration where there are multiple SPB-shapedcompartments for a single SPB 300, the compartments being the wide,balloon-shaped portions. By “SPB-shaped” it is meant that the shape isgenerally similar to that of the SPB 300 described herein, for examplewith respect to FIGS. 3A and 3B, but need not be the exact shape norinclude all features thereof. FIG. 9C depicts an embodiment of an LTAsystem 102 having two SPB's 300. FIG. 9D depicts an embodiment of an LTAsystem 103 having three SPB's 300. FIG. 9E depicts an embodiment of anLTA system 103 having four SPB's 300. Some embodiments of the LTAsystems may have more than four SPB's 300.

To reach design goals, for example with the performance ratio Rdescribed above, as the balloon system gets larger, using only a singlepumpkin ballast balloon SPB 300 may not be desirable. For instance, forsome missions there may be a strength limitation or a stabilitylimitation with only a single SPB 300. An alternative is stacking theSPB's 300. This may not be as weight efficient as a single SPB 300, buta single SPB 300 may have structural or stability issues, such asS-clefting. Multiple smaller SPB's 300 may address these issues.Examples of LTA systems having two, three and four SPB's 300 are shownrespectively in FIGS. 9C, 9D and 9E.

A possible advantage of a second or third or fourth or more SPB 300, orof a single SPB 300 with multiple compartments, in the system is themaximum diameter and thus volume of the SPB 300 is constrained by thehoop stress of the material it is made of. Thus, one possible way toincrease ballast volume is to have multiple discrete SPBs in the system.In another embodiment, instead of each SPB being discrete (e.g., formedas separate units that are coupled (mechanically and/or fluidly)together), chambers of the SPB are interconnected through a constrainedchamber and form a configuration having the visual appearance of a“sausage.” Each sausage section then can attain maximum radius for hoopstress, with all chambers connected via the constriction between links.Such an LTA system may comprise a ZPB 200 plus one or more suchsausage-configured SPBs 300.

The LTA systems with multiple SPB's 300, such as the LTA systems 102,103, 104, may have any or all of the same or similar features and/orfunctionalities as the other LTA systems described herein, such as theLTA systems 100 or 101, and vice versa. The SPB's 300 may include one ormore SPB's that form one large, fluidly connected volume that has thevisual appearance of multiple SPB's (e.g., a “sausage” configuration).Thus, some or all of the SPB's 300 may be in fluid communication witheach other. In some embodiments, the multiple SPB's 300 may not be influid communication with each other. For example, rope rings, metalfittings, etc. may separate the internal air compartments of each SPB300. Each of the multiple SPB's 300 may be referred to as “SPBcompartments” that make up the SPB 300. The SPB 300 may comprise two ormore of the SPB compartments. The “compartments” refer to the enlargedportions of the SPB 300 having the general shape of the single SPB 300,for example as shown in FIG. 1. Thus, FIG. 9C shows two SPBcompartments, FIG. 9D shows three SPB compartments, and FIG. 9E showsfour SPB compartments. The SPB 300 may include the SPB compartmentsconnected in series as shown in FIGS. 9C-9E. In some embodiments, theSPB compartments may be connected in series, in parallel, in otherconfigurations, or combinations thereof. The two or more SPBcompartments of the SPB 300 may or may not be in fluid communicationwith each other. In some embodiments, some of the SPB compartments ofthe SPB 300 may be in fluid communication with some of the other SPBcompartments but not in fluid communication with other of the SPBcompartments. The multiple SPB's 300 may be formed separately and thenconnected together. In some embodiments, the multiple SPB's 300 areformed from the same continuous skin and are either fluidly connected orare “tied off” from each other using the rope rings, metal fittings,etc. There may be a single compressor assembly 800 that provides ambientair to all of the SPB's 300, for example with multiple air hoses 690 orwith a single air hose 690 where the multiple SPB's 300 are fluidlyconnected. In some embodiments, each SPB 300 may have its own compressorassembly 800 or compressor 810, and/or its own valves 870 and/or 871.Thus, each SPB 300 may have its own discrete air intake and releaseassembly. These are merely some examples of the multiple SPB 300embodiments of the LTA system and how they may be implemented, andothers not explicitly described herein are within the scope of thedisclosure. For example, five or more SPB's can be used, the multipleSPB's need not be configured in a single line (e.g., the system caninclude hardware from which at least some of the SPB's are coupledlaterally relative to each other), etc.

J. Mission-Specific Platforms

The particular configuration of the LTA system 100 and the method of usecan be based on the mission. The various missions may include, forexample, lower altitude missions, higher altitude missions,station-keeping, meteorological purposes, heavy payload lifting, shortduration missions, long duration missions, constellations, handoffs,racetrack, and others. For these and other missions, the LTA system 100and/or the method of use of the LTA system 100 can be accordinglyconfigured.

For example, the LTA system 100 can be configured for higher altitudeand/or heavy payload lifting by including larger volume ZPB 200 and SPB300 and/or the compressor 810 having a larger mass flow rate at lessdense and lower pressure atmospheres. Thus, for higher altitude and/orheavy payload lifting, the LTA system 100 may have a multi-stagecompressor 810, such as a two-stage compressor 810, a ZPB 200 having aninternal volume of about 30,000 cubic meters, and a SPB 300 having aballast capability of +/−100 kilograms. Further, the release valves 870and/or 871 can be configured to allow for a faster mass flow rate, suchas with a larger opening 877 and/or 878 and/or with multiples valves 870and/or 871. Such a system may allow for reaching higher altitudes,larger altitudinal ranges, and doing so at faster speeds.

As another example, the LTA system 100 can be configured for loweraltitude and/or lighter payload lifting by including smaller volume ZPB200 and SPB 300 and/or the compressor 810 having a smaller mass flowrate. This may provide for a lower mass and less complex system. Thus,for lower altitude and/or lighter payload lifting, the LTA system 100may have a single-stage compressor 801, a ZPB 200 having an internalvolume of about 700 cubic meters, and a SPB 300 having a ballastcapability of about +/−50 kilograms. Further, fewer and/or smallerrelease valves 870 can be used, also saving on mass and complexity. Sucha system may allow for reaching lower altitudes and at less cost due tomass savings and less complexity with design of the LTA system 100.

K. Control System

FIG. 10 is a schematic an embodiment of a control system 1000 that maybe used with the various LTA systems described herein, for example theLTA system 100 and 101. In some embodiments, the control system 1000 isin communicating connection with the sensor 740, with the centrifugalcompressor 810, and with the adjustable valve 740, and is configured tocontrol the centrifugal compressor 810 and the adjustable valve 740based at least on one or more detected environmental attributes tocontrol the amount of ambient air inside the SPB 300 to control analtitude of the LTA system 100.

The control system 1000 includes a controller 1010 in communicatingconnection with various components. The communicating connections may bewired or wireless. The controller 1010 is an electronic controller. Thecontroller 1010 is in communicating connection with one or more sensors1020. The sensor 1020 may be the sensor 740 described herein. The sensor1020 detects various parameters and provides corresponding output, forexample data or information, that is communicated to the controller1010. The controller 1010 receives the output from the sensor 1020 todetermine various control operations.

The controller 1010 is in communicating connection with a valve 1030 anda compressor 1040. The valve 1030 and the compressor 1040 may be,respectively, the valve 870 and the compressor 810 described herein. Thevalve 1030 and compressor 1040 are shown as separate components. In someembodiments, the valve 1030 and compressor 1040 may be part of the samesystem, such as the compressor assembly 800 or part of a reversiblecompressor, as described herein. The controller 1010 controls theopening and closing of the valve 870 to cause more or less air to bereleased from the SPB 300. The controller 1010 controls the operation ofthe compressor 810 to cause more or less air to be provided to the SPB300, for example by running the compressor at higher or lower speeds.

The controller 1010 may control the operation of the valve 1030 and/orcompressor 1040 based on output of the one or more sensors 1020, and/orbased on commands sent to the controller 1010 via a communicationssubsystem. For example, light sensors, pressure sensors, thermalsensors, and/or other sensors may detect daylight, ambient pressure,ambient temperature, and/or other parameters, that are analyzed by thecontroller 1010 to control the valve 1030 and/or compressor 1040. Thecontroller 1010 may determine, based on data detected with the sensors1020 and/or received communication signals, that a lower altitude isrequired. Thus, the controller 1010 may send a control signal to thecompressor 1040 to cause the compressor 1040 to provide more air to theSPB 300 to cause the LTA system 100 to descend. Alternatively, thecontroller 1010 may determine, based on data detected with the sensors1020 and/or received communication signals, that a higher altitude isrequired. Thus, the controller 1010 may send a control signal to thevalve 1030 to cause the valve 1030 to release air from the SPB 300 tocause the LTA system 100 to ascend. Further, the controller 1010 maycontrol, in the manner discussed, the rate of air intake or air releasein order to control, respectively, the rate of descent or ascent of theLTA system 100.

The controller 1010 is in communicating connection with a gimbal 1050.The gimbal 1050 may be the gimbal 500 described herein. The controller1010 controls actuation of the gimbal 1050, for example actuation of themotor 510 of the gimbal 500. The controller 1010 controls actuation ofthe gimbal 1050 to control relative rotation of the ZPB 200 and SPB 300,for example to point the solar array 630 is a particular direction. Thecontroller 1010 may control actuation of the gimbal 1050 based on outputof the sensor 1020, and/or based on commands sent to the controller 1010via a communications subsystem. For instance, light detectors, timers,global positioning systems (GPS), LTA system locators that are separatefrom but which communicate with the LTA system 100, and/or other sensors1020, may provide data output or communications to the controller 1010.The controller 1010 may determine, based on data detected with thesensors 1020 and/or received communication signals, that rotation of thesolar array 630 is required. The controller 1010 may then send a signalto the gimbal 1050 to actuate a particular amount. For instance, thecontroller 1010 may send a control signal to the gimbal 500 to cause themotor 510 to operate at a particular speed and/or for a particularamount of time. In some embodiments, the data is detected with thesensors 1020, and/or the communication signals are received,continuously or at regular intervals, such as during daylight, andprovided to the controller 1010 for continuous or interval control ofthe solar array 630. Such operations may allow, for example, fortracking of the sun with the solar array 630 for optimal energyconversion.

The controller 1010 is in communicating connection with a payload 1060and supporting subsystems 1070. The payload 1060 may be the payload 730described herein. The supporting subsystems 1070 may be the varioussubsystem described herein, for example communications subsystem,release mechanisms, etc. The controller 1010 controls various operationsof the payload 1060 and supporting subsystems 1070, for examplegathering data with an optical instrument, taking readings with varioussensors of the subsystems, transmitting and receiving information to andfrom ground stations, satellites, other balloon systems, etc. Thecontroller 1010 may control the payload 1060 and supporting subsystems1070 based on output of the sensor 1020, and/or based on commands sentto the controller 1010 via a communications subsystem. For instance, thecontroller 1010 may send a control signal to the payload 730 to take asample or reading with an optical instrument. As further example, thecontroller 1010 may receive a communication signal to release thepayload support 700, and the controller 1010 may then send a controlsignal to one or more release mechanisms to cause the payload support700 and parafoil 680 to separate from the upper craft 600.

L. Navigation and Control Methods

FIGS. 11-12 depict embodiments of various flight aspects, for examplemaneuvers, trajectories, speeds, etc., that may be performed with thevarious LTA systems described herein, for example with the LTA system100 and 101. Only some example flight aspects of the LTA system 100 aredescribed, and the LTA system 100 has other flight aspects even thoughnot explicitly described. Although the flight aspects are described inthe context of the LTA system 100, it is understood that these aspectsapply equally to other LTA systems described herein, including the LTAsystem 101.

1. Ascent and Descent

FIG. 11A is a schematic depicting embodiments of ascent rates, descentrates and flight ranges that the LTA system 100 is capable of achieving.These aspects are described with reference to various variables for thesake of description only. The aspects shown are approximations togenerally show capability. The LTA system 100 is not limited by thisexample schematic. For instance, the LTA system 100 may ascend higherthan 120,000 feet. As shown, the LTA system 100 begins at point A on theground and ascends to point B at 50,000 feet (“50 k” feet), then ascendsto point C at 100 k feet, and then ascends to point D at 120 k feet. TheLTA system 100 then descends from point D at 120 k feet to point E at100 k feet, then descends to point F at 50 k feet, and then descendsback to ground at point G. The flight path shown from point A to point Gand described herein is for illustrative purposes to show the variouscapabilities of the LTA system 100. The LTA system 100 may follow theflight path shown or other flight paths. In some embodiments, the LTAsystem begins at point A and ascends to point D, then cyclicallydescends and ascends to and from points D and E. In some embodiments,the LTA system begins at point A and ascends to point D, then cyclicallydescends and ascends to and from points D and F. In some embodiments,the LTA system begins at point A and ascends to point C, then cyclicallydescends and ascends to and from points C (or E) and B (or F). After anumber of these or other cycles at high altitude, the LTA system 100 mayrelease the payload support 700 with the parafoil 680 for controlledflight to ground, and the ZPB 200 and SPB 300 may terminate theirflights and fall back to ground, either together or separately.Alternatively, after a number of these or other cycles at high altitude,the entire LTA system 100 may descend back to ground together, throughpoint F to point G. Various sample capabilities of time of flight andspeed of the LTA system 100 for the various ranges and altitudes shownin FIG. 11A are provided in Table 1.

TABLE 1 Sample capabilities of the LTA system for the various ranges andaltitudes shown in FIG. 11A. Altitude Range Time Max Speed Location(feet) (feet) (hours) (feet/hour) A → B  0 → 50k +50k T_(A) → T_(B) =7.8 V_(AB) = 19,200  B → C  50k → 100k +50k T_(B) → T_(C) = 4.3 V_(BC) =21,600  C → D 100k → 120k +30k T_(C) → T_(D) = 4   V_(CD) = 5,000  D → E120k → 100k +30k T_(D) → T_(E) = 4   V_(DE) = −5,000  E → F 100k → 50k −50k T_(E) → T_(F) = 4.6 V_(EF) = −13,200 F → G 50k → 0  −50k T_(F) →T_(G) = 5.0 V_(FG) = −30,000

FIG. 11B is a flow chart showing an embodiment of a method 1100 forascending and descending with the LTA system 100. The method 1100 may beperformed for example to achieve the ascent and descent rates and rangedescribed with respect to FIG. 11A. The method 1100 may be performedwith the various LTA systems described herein, including the LTA systems100 and 101, and other variations of those LTA systems.

As shown in FIG. 11B, the method 1100 begins with step 1110 wherein aZPB is connected with a pumpkin-shaped SPB. Step 1110 may include theZPB 200 being connected with the SPB 300 in its pumpkin shape orconfigured to be in its pumpkin shape. In step 1110 the ZPB 200 may beconnected directly to the SPB 300, or they may be indirectly connectedfor example via the gimbal 500 or 501. In step 1110 the ZPB and SPB maybe connected in an assembly facility, at the launch pad, or in othersuitable locations.

The method 1100 then moves to step 1120 wherein a centrifugal compressorand valve are fluidly connected with the SPB and with the ambient air.Step 1120 may include the compressor assembly 800 and the valve 870being connected with the SPB 300 via the air hose 690. Step 1120 mayinclude the compressor assembly 800 and the valve 870 being connectedwith the SPB 300 via the air hose 690. The connections may be open suchthat air may flow freely or closed, for example where the valves 870 or871 are closed when connected. Thus, “fluid” connection in step 1120means capable of being in fluid connection. In step 1120 the centrifugalcompressor and valve may be fluidly connected with the SPB and with theambient air in an assembly facility, at the launch pad, or in othersuitable locations.

The method 1100 then moves to step 1130 wherein lift gas is provided tothe ZPB. Step 1130 may include LTA lift gas, such as helium or hydrogen,being provided to the ZPB 200. The LTA gas may be provided to the ZPBvia hose or other suitable means. The various volumes and amounts of LTAgas described herein may be provided in step 1130.

The method 1100 then moves to step 1140 wherein the ZPB 200, SPB 300,compressor 810 and valve 870 are launched to high altitude. Step 1140may include launching to high altitude the LTA system 100 including theZPB 200, the SPB 300, the compressor 810 and the valve 870. Step 1140includes the ZPB 200 with lift gas therein providing the lift to thevarious components. Step 1140 may include the ZPB 200 lifting thevarious components to the upper troposphere, the tropopause and/or thestratosphere.

The method 1100 then moves to step 1150 wherein air is pumped into theSPB 300 with the compressor 810 to descend the ZPB 200, SPB 300,compressor 810 and valve 870. Step 1150 may include the compressor 810pumping air from the surrounding atmosphere at high altitude into theSPB 300 via the air hose 690. Step 1150 may include the LTA system 100descending due to the increased mass of air in the SPB 300, as describedherein. The LTA system 100 may descend in step 1150 as described forexample with respect to FIG. 11A.

The method 1100 then moves to step 1160 wherein air is released from theSPB 300 with the valve 870 to ascend the ZPB 200, SPB 300, compressor810 and valve 870. Step 1160 may include the valve 870 releasing airfrom the SPB 300 via the air hose 690 into the surrounding atmosphere athigh altitude. Step 1160 may include the LTA system 100 ascending due tothe decreased mass of air in the SPB 300, as described herein. The LTAsystem 100 may ascend in step 1150 as described for example with respectto FIG. 11A.

The method 1100 may be repeated in various manners. For example,multiple LTA systems 100 may be launched and flown as described in themethod 1100. As further example, steps 1150 and 1160 may be repeatedafter performing steps 1110 to 1140. In some embodiments, some or all ofthe steps of the method 1100 may be performed, and the flight may beterminated, for example in the various manners described herein. Forexample, steps 1110 to 1140 may be performed and then steps 1150 and1160 may be cyclically repeated multiple times, after which the LTAsystem 100 flight may be terminated as described.

The LTA system 100 can be used for a variety of different missions. TheLTA system 100 can be used to remain airborne for longer durations, forexample during stratospheric flights with sustained communications. TheLTA system 100 can be used to maintain a fairly constant footprint onthe ground, particularly in the case of observation and communications.The LTA system 100 thus enables altitude maintenance during diurnalvariations in solar elevation as well as station-keeping for largeportions of the year worldwide. Some embodiments of a station-keepingpersistence envelope with active altitude control that may be performedwith the LTA system 100 are described herein.

2. “Barber Pole” Station-Keeping

FIG. 12A is a schematic depicting an embodiment of a persistenceenvelope for high altitude station-keeping with the LTA system 100. Theenvelope includes an upper portion of the troposphere, the tropopause,and the stratosphere. Boundaries between these layers of the upperatmosphere are indicated by the two dashed lines.

As shown in FIG. 12A, the LTA system 100 begins at point J in the uppertroposphere. The LTA system 100 then travels from point J to point Kalong the path X₁. The LTA system 100 travels along the path X₁ due tothe prevailing winds. Point K is approximately at the same altitude aspoint J. In some embodiments, point K may be at a different altitudethan point J. The point K corresponds to latitude and longitudecoordinates within a first range of latitude and longitude coordinates.The first range of latitude and longitude coordinates may correspond tofavorable locations of the tropopause through which it is desirable forthe LTA system 100 to ascend. At point K, the LTA system 100 ascends.The LTA system 100 ascends by releasing air, for example by controllingthe valve 870 to release air from the SPB 300. The LTA system 100 maythen ascend from the upper troposphere and into the tropopause.

The LTA system 100 ascends through the troposphere along the path Y₁.The path Y₁ is a helix or an approximate helix through the tropopause.Thus, the LTA system 100 ascends along a helical path, or “barber pole.”The trajectory that the LTA system 100 travels is helical through thetropopause because of the first range of latitude and longitudecoordinates correspond to a portion of the tropopause having varyingwind directions at different altitudes. It should be noted that varyingwind directions may be found in all parts of the atmosphere, and “ridingon the barber pole” is not limited to operations only in the tropopause.The LTA system 100 can thus take advantage of varying wind directionsanywhere within its altitude changing range. Thus, the descriptionherein of the helical path with respect to particular portions of theatmosphere, such as the tropopause, is not meant to limit the use of theLTA system 100 in that manner to only those areas.

The wind directions in the tropopause, and/or in other portions of theatmosphere, angularly vary at varying altitude such that the LTA system100 travels along the helical path. The path Y₁ has an approximatediameter D₁ as indicated. The diameter D₁ varies depending on the speedof the winds and the rate of ascent of the LTA system 100. The rate ofascent can be controlled based on the rate of release of air from theSPB 300. Thus, the diameter D₁ of the helical path Y₁ can be affected bycontrolling the rate of release of air from the SPB 300. For example,air may be released at a relatively slower rate such that the LTA system100 ascends at a relatively slower rate. Thus, the LTA system 100 willspend more time in any one of the various layers of the tropopausehaving varying wind directions, and so the helical path Y₁ will have alarger diameter D₁. Conversely, for example, air may be released at arelatively faster rate such that the LTA system 100 ascends at arelatively faster rate. Thus, the LTA system 100 will spend less time inany one of the various layers of the tropopause (or any part of theatmosphere the LTA 100 system is operating) having varying winddirections, and so the ideally helical path Y₁ will have a smallerdiameter D₁. By varying the speed of ascent or descent of the LTA system100, these helical trajectories can be modified so that the flight stayswithin a desired range of latitude and longitude coordinates.

At point L, the LTA system 100 stops ascending. For example, the LTAsystem 100 may stop releasing air from the SPB 300. As further example,the LTA system 100 may have already stopped releasing air and the LTAsystem has now reached its maximum or equilibrium altitude. From pointL, the LTA system travels along the path X₂ to point M. The path X₂ isin a different direction than that of the path X₁. In some embodiments,the path X₂ is in the opposite direction than that of the path X₁. Thepoint M is at the same or similar altitude as the point L. In someembodiments, the point M may be at a different altitude than the pointL.

The point M corresponds to latitude and longitude coordinates within asecond range of latitude and longitude coordinates. The second range oflatitude and longitude coordinates may correspond to favorable locationsof the tropopause through which it is desirable for the LTA system 100to descend. The second range of latitude and longitude coordinates mayinclude all, some or none of the coordinates within the first range oflatitude and longitude coordinates. For example, the first and secondrange of latitude and longitude coordinates may be identical. As furtherexample, the first and second range of latitude and longitudecoordinates may share some of the same coordinates, i.e. may beoverlapping. As further example, the first and second range of latitudeand longitude coordinates may not share any of the same coordinates,i.e. may be entirely separate and not overlap at all. At point L, theLTA system 100 descends. The LTA system 100 descends by moving air intothe SPB 300, for example by controlling the compressor 810 to causeambient air from the surrounding atmosphere to flow into the SPB 300.The LTA system 100 may then descend from the upper troposphere and intothe tropopause.

The LTA system 100 descends through the troposphere along the path Y₂.The path Y₂ is a helix or an approximate helix through the tropopause.The path Y₂ travelled by the LTA system 100 is similar to the path Y₁but in the opposite direction, and possibly at different latitudes andlongitudes than the path Y₁. Thus, the LTA system 100 descends along ahelical path Y₂, or “barber pole.” The trajectory that the LTA system100 travels is helical through the tropopause because the second rangeof latitude and longitude coordinates corresponds to a portion of thetropopause having varying wind directions at different altitudes. Thewind directions angularly vary at varying altitude such that the LTAsystem 100 travels downward along the helical path Y₂. The path Y₂ has adiameter D₂ as indicated. The diameter D₂ varies depending on the speedof the winds and the rate of descent of the LTA system 100. The rate ofdescent can be controlled based on the rate air intake into the SPB 300.Thus, the diameter D₂ of the helical path Y₂ can be affected bycontrolling the rate of air intake into the SPB 300. For example, thecompressor 810 may be operated at a relatively slower speed such thatair is taken in at a relatively slower rate, so that the LTA system 100descends at a relatively slower rate. Thus, the LTA system 100 willspend more time in any one of the various layers of the tropopausehaving varying wind directions, and so the helical path Y₁ will have alarger diameter D₂. Conversely, for example, air may be taken into theSPB 300 at a relatively faster rate such that the LTA system 100descends at a relatively faster rate. Thus, the LTA system 100 willspend less time in any one of the various layers of the tropopausehaving varying wind directions, and so the helical path Y₁ will have asmaller diameter D₂.

After descending through the tropopause along the path Y₂ and into theupper troposphere, the LTA system 100 stops descending. For example, theLTA system 100 may stop descending by ceasing to take in more air intothe SPB 300. As further example, the LTA system 100 may have alreadystopped taking in air into the SPB 300 and the LTA system 100 has nowreached a minimum or equilibrium altitude. The LTA system may exit thetropopause and stop ascending in the upper troposphere after returningto point J, as shown. In some embodiments, the LTA system may exit thetropopause and stop ascending in the upper troposphere at a point otherthan at point J. For example, the LTA system 100 may stop ascending at adifferent altitude than point J. As further example, the LTA system 100may stop ascending at a same altitude as point J but laterally at adifferent location, i.e. at different latitude and/or longitudinalcoordinates. As another example, the LTA system may stop ascending at adifferent altitude and at a different lateral position than point J.

From point J, or from another point where the LTA system stopsdescending, the LTA system may travel laterally within the uppertroposphere. As shown, the LTA system 100 may travel from point J alongthe path X₁ to point K. In some embodiments, the LTA system 100 maytravel along a path different from the path X₁. In some embodiments, theLTA system 100 may travel from point J along a path to latitude andlongitude coordinates that are different from point K but which arewithin the first range of latitude and longitude coordinates. In someembodiments, the LTA system 100 may travel from point J to a locationthat is not within the first range of latitude and longitudecoordinates.

3. Altitude Control Coverage Patterns

A variety of different trajectories may be flown with the LTA system 100to establish persistent coverage. This section presents three altitudecontrol coverage patterns that can be used with the LTA system 100 toprovide persistent coverage over an area of interest (AOI). Thesepatterns are the Single Pass Coverage (SPC), Multiple Pass OrbitalCoverage (MPOC), and the Station-Keep Coverage (SKC) flight patterns. Toprovide persistent coverage, these patterns may be used in combination.Prior to a mission, forecasting tools, wind scoring (see below), etc.may be used to establish the coverage patterns needed to meetpersistence requirements and hence identify the launch locations andlaunch frequencies (i.e., constellation requirements). The trajectorysimulations presented show four scenarios where SKC and MPOC coveragepatterns are applicable. In all cases, the SPC flight pattern may beused, but may not be the most cost effective option.

The LTA system 100 offers a platform with direct line of sight (LOS)coverage of an area of interest (AOI) for extended durations. The LTAsystem 100 may have its trajectory altered so as to remain within directLOS of the AOI. The LTA system 100 can accomplish this by ascending ordescending to different altitudes that hold wind speeds and directionsfavorable to a return trajectory. A given mission will require directLOS coverage for distinct periods of time separated by intervals with nocoverage. Meeting this schedule of direct LOS coverage is defined aspersistent coverage.

To establish persistent coverage over an AOI, the LTA system 100provides ascent and descent rate capabilities over an altitude rangethat encompasses a variety of wind directions. Many factors go intodetermining the degree to which persistent coverage over a region ispossible, as well as the methods and costs involved in doing so. Theprimary factors include the AOI ‘regional’ winds and the time of year ofthe operation. The proposed operating regime here is within the uppertroposphere, the tropopause and the stratosphere. In the stratosphere,average wind patterns vary from month to month and from location tolocation. These and other features of the upper atmosphere areadvantageously used by the LTA system 100.

Of particular significance to flight of the LTA system 100 at highaltitudes is the characterization of wind speed and direction withlocation, altitude, and time of year. The general wind patterns based onaltitude and time of year present an organizational structure. Thisorganizational structure allows one to roughly establish the altitudechange required to “station-keep” over any given place for any givenmonth.

Our typical experience with winds is naturally tied to the troposphere,where regional conditions, and localized convection made possible by thetropospheric temperature gradient, create a chaotic wind environment.The altitude of the tropopause varies. It is approximately 15 km (˜120mb) in the equatorial region and 9 km (˜300 mb) in the polar region. Aswe go higher into the atmosphere, the regional differences have lesseffect, and broader patterns emerge. Within the stratosphere, winds aregenerally driven by the global distribution of absorbed solar heat, andthe Coriolis effect. Near the equator, upper winds almost always blowprimarily out of the east, with increasing variability pole-wards.Winter at the given pole tends to result in very strong winds blowingout of the west (westerly), while a polar summer tends to result inslower, more varied, easterly winds. The change in direction, referredto as the ‘turnaround’, occurs twice a year, typically May and October.

The Single Pass Coverage (SPC) pattern is used with the LTA system 100if no circulatory pattern exists in the region about the AOI. In thisscenario, the LTA system 100 would be launched at a point upwind,allowed to float over the AOI, and then returned to the ground at apoint downwind of the AOI. Multiple launch and recovery options areafforded by the use of the altitude control capabilities of the LTAsystem 100. Although this tactic can always be used, it is the mostexpensive option as multiple LTA systems 100 will need to be deployed tomeet the mission persistence requirement.

The Multiple Pass Orbital Coverage (MPOC) pattern can be used with theLTA system 100 if a circulatory pattern exists in the region about theAOI that allows the LTA system 100 to return back over the AOI multipletimes. The circulation does not need to be continuous in a singlestratum, as the return trajectory can take place over multiple strata.The size of the loop and the persistence requirement will dictate thenumber of LTA systems 100 that must be flown. This option can greatlyreduce hardware and operations cost for long duration missions.

The Station-keep Coverage (SKC) pattern can be used with the LTA system100 when wind speeds over the AOI are low and the direction is variable.Under these favorable conditions, a balloon can loiter over an AOI foras long as the weather pattern supports it.

These different coverage patterns are necessary to accommodate thevariability in local wind pattern from location to location and the timeof year. In addition, long duration missions may occur across severalweather patterns and thus require a combination of deployment tactics tomeet persistence objectives. Opportunities to fly the MPOC and SKCcoverage patterns improve when the winds are slow and varied. SPC may bepreferably used when the winds are uniformly directional at alloperational altitudes. The ability to change altitude can improve thechance for cost-efficient persistence coverage maneuvers if the windvectors are favorable at the other altitudes. For instance, the windpattern at the higher altitudes, e.g., 10 mb and 20 mb, do not differmuch. The main difference between these two altitudes is in velocitymagnitude. The probability of finding different wind directions improveswhen the operating range is extended down to 100 mb. These observationsare based on averaged velocities and actual winds may offer greateropportunities.

A mission plan for the LTA system 100 would begin with a review ofhistoric wind data to determine if altitude control balloon technologyis applicable. The probability for having light and variablestratospheric winds varies by location and time of year but in generalthere exists a fairly high probability of station keeping windsworld-wide throughout a large portion of the year. If the LTA system 100is appropriate, the mission plan would then focus on the coveragepatterns available to establish persistent coverage. The mission planwould be based on wind analyses of actual forecasted data and trajectorysimulations performed in the weeks leading up to the mission, for theAOI and time of interest. The plan would be periodically revised withupdated forecast data. It would be necessary to continue these revisionsinto the mission itself for long duration missions. LTA system 100trajectory calculations would be based on actual forecasted wind datathat resolve both spatial and temporal differences around the AOI.

Prior to doing trajectory simulations for the LTA system 100, theforecasted winds would be processed to determine if MPOC and SKCcoverage patterns are feasible and if so to what extent. Computeranalysis tools may be used to process historic data and forecast data tohelp identify and/or visualize the likely locations, times, and moreimportantly the altitudes by which MPOC and SKC patterns are possible,or if the mission must be accomplished with the SPC pattern. Thesoftware may analyze the raw radiosonde data using data analysis modulesto determine the types of wind. The winds are characterized in 3 types:Type 0a, Type 1 and Type 2. Type 0a refers to light and highly variablewinds spanning the compass within a defined region. Type 1 refers tobalanced winds in both directions of zonal and meridional flow. Type 2refers to stable, optimal zonal shear pattern winds.

The mission plan for the LTA system 100 would be finalized by performingtrajectory simulations using actual forecasted wind data. Thesesimulations would identify the coverage patterns (SPC, MPOC, and/orSKC), launch locations and timing, and approximate recovery locationsand timing. The trajectory simulations employ a fourth-order Runge-Kuttaintegration scheme to calculate trajectory from acceleration andvelocity. Wind speed and direction are linearly interpolated in timefrom one-time period to the next (6 hours apart), linearly in latitudeand longitude, and using a continuously differentiable Akima spline inaltitude. Balloon ascent and descent rates can either be assumedconstant or determined through the solution of the complete set of LTAsystem 100 performance governing equations (force and heat balanceequations). Ascent and descent commands can either be input manually(flight simulator mode) or using an auto-pilot control algorithm.

In cases where the operating altitude for the LTA system 100 over theAOI is prescribed due, for example, to specific sensor requirements, itmay not be possible to use SKC even if wind conditions accommodated suchan operation over the AOI. In these cases, SPC or MPOC will be used,however the principals of SKC become highly advantageous to the overalloperation when the vehicle is not in the AOI. For example, the SKC windpatterns could greatly simplify SPC operations by allowing the LTAsystem 100 to be launched from a base or ship, navigate to the up-windlocation for entering the AOI, and then ascend or descend to theoverflight operating altitude for the fly-over. Clearing the AOI, theLTA system 100 can then use the winds to maneuver within range of thelanding site to potentially navigate around the AOI in an MPOCoperation.

4. Wind Data Analyses

Identification of the various regions of the upper atmosphere havingfavorable wind conditions may be based on a variety of approaches. Insome embodiments, the sensors 740 may provide data related to winddirection, temperatures, pressures, etc. that assist with determiningthe ideal wind conditions. In some embodiments, data from other LTAsystems 100 already in flight may provide information regions with idealwind conditions. For instance, multiple LTA systems 100 may be used in aconstellation, and data gathered from each LTA system 100 may beanalyzed to inform the other LTA systems 100 in the constellation ofideal wind condition locations. In some embodiments, data may bereceived from non-LTA system balloons that are in flight. In someembodiments, data may be received from meteorological instruments, suchas from satellites or ground systems.

In some embodiments, these and/or other sources of data, in conjunctionwith the basic system design of the LTA system 100, may be used forachieving enhanced guidance, navigation and control (GNC) as compared totypical LTA systems. In some embodiments, such enhanced GNC is achievedby the combination of the advanced features of the LTA system 100 forrapid descent/ascent, along with analysis of a mission planning based oncertain wind data. Such wind data may include data on the varying windspeeds and directions stratified within the troposphere, tropopause,and/or stratosphere. For example, at certain times of the year, and incertain locations that are less conducive to station-keeping operations,the LTA system 100 allows for constellation flight operations tomaintain constant line of site with multiple tandem balloon systemfly-overs. In some embodiments, this and/or other data is used toproduce “wind scores” for GNC purposes.

The LTA system 100, for example the control system 1000, can analyzeglobal winds at high altitudes, for example in the stratosphere, todetermine optimal station-keeping navigation around the world and yearround. The LTA system identifies long-term patterns from winds that arevariable, shifting and unpredictable over the short term. In someembodiments, the LTA system 100 analyzes such data and determines overlong periods that radiosonde data of winds may vary greatly only 12hours apart in the same location, but that there are exploitablelonger-term patterns that persist for days or weeks and are consistentfrom year to year.

The LTA system 100 and/or supporting systems such as ground stationsanalyzes the various data about winds and identifies corresponding GNCcontrol algorithms and techniques for optimal flight. For instance,zonal winds (east/west) typically have a very consistent pattern overthe course of a year. In many places, particularly latitudes between 20and 60 degrees north and south, zonal winds blow predominantly in onedirection at low altitudes, then cross over to the opposite direction inthe lower stratosphere, then generally switch back to the originaldirection higher in the stratosphere. Equatorial and polar conditionscan be less predictable.

Meridional winds are far more chaotic. However, some patterns arepresent, in two ranges. The upper range is characterized bypredominantly north or south winds, with small pockets of the oppositedirection interspersed unpredictably (in time and space) throughout.Within the lower range (from roughly 20 km down to the aviationrestriction boundary) a condition of strong meridional wind, in onedirection or another, is frequently present. Such winds may beidentified that exist strongly within a particular altitude and do notchange any further in the wind column downwards. The pattern may be thatthe winds blow north for a week, are neutral for a week, blow south fora week, and so forth. The LTA system 100 or related systems may identifyor determine a signature, or fingerprint, that is fairly unique to eachregion based on analysis of the winds over longer periods, for instanceover the course of a year. The LTA system 100 may determine that thezonal winds are fairly consistent and predictable, and the meridionalwinds are mostly chaotic in the upper range, with odd bands of periodicresonances (on the order of a week or so) present in the lower range.The LTA system 100, for example the control system 1000, may determine anavigational trajectory accordingly.

Trajectories for the LTA system 100 may be determined based on variouswind scoring or rating approaches. One such approach is described here.Medium period wind patterns, currently defined as being significant for12-60 hours, are particularly important when it comes to meridionalnavigation, since those winds shift so quickly and randomly. In thisperiod, the GNC and related control algorithms of the LTA system 100 mayanalyze regions of air, not particular heights. In order to define thesewind regions, the wind scoring algorithm starts with a simple weightedmoving average over a set of vertical samples, which may be for examplefrom nearby radiosonde flights, or from the LTA system 100 flightitself, such as sensors 740. The weighting may be a simple linear weightbased on the distance from the center sample. Distances further than 500meters may be ignored. A fixed window of nine samples may be used. Greenregions (light and variable) are identified by having a weightedstandard deviation greater than the magnitude of their mean, on bothhorizontal axes, across a span of altitudes. They are presently scoredfor their “quality” by scaling their mean winds by the ratio of theirstandard deviation to their mean, on each axis, and summing the tworesults. This emphasizes the primary importance of low mean windmagnitude, while secondarily taking into account wind turbulence, lowerscores obviously making them better green regions. It is the absolutevalue of the mean that the algorithm is looking for, in this case. Thealgorithm rates these winds using a “green score,” which may bedetermined as shown here:

${{{green}\mspace{14mu}{score}} = {{Z_{mean}( \frac{Z_{mean}}{Z_{std}} )} + {M_{mean}( \frac{M_{mean}}{M_{std}} )}}},{Z_{std} > {Z_{mean}}},{M_{std} > {{M_{mean}}.}}$

Green winds may be an optimal area to remain in for station-keeping, asit signifies a likelihood that that many wind directions can be found.Further, in this area the winds are consistently blowing at low speeds,which may be about five meters per second or less.

This is merely an example of how wind data may be analyzed and used bythe LTA system 100. Other approaches may be implemented, including butnot limited to those described, for example, in U.S. provisional patentapplication No. 62/294,204, entitled SEMI-AUTONOMOUS TRAJECTORY CONTROLFOR BALLOON FLIGHT and filed Feb. 11, 2016, the entire disclosure ofwhich is incorporated by reference herein for all purposes. Forinstance, “yellow” and “blue” regions may be identified, as describedtherein, that omit the other horizontal axis in the calculation.

The GNC algorithm may comprise multiple layers. At the highest level, isthe overall mission intent, be it station-keeping, or path control.Below that is the direction layer. The mission layer consists of anobjective, and considers the present location of the balloon. Theobjectives can be to station-keep within a particular range, or totravel to a particular nearby location (within a few hundred kilometers;accuracy best if direction is primarily zonal). One example of aprocedure is described below:

1. The mission for the LTA system 100 is planned, and long-termparameters may be set, based on observation of long-term trends.Tolerances of station keeping are specified by maximum range separatelyin zonal and meridional directions to accommodate the disparity in windavailability (typically much more zonal slack than meridional, as zonalposition is easier to fix, and it's often necessary to drift off-centerzonally in order to correct meridional position).

2. On-board system may maintain a set of wind observations, recordingspeed, direction, and timestamp. Some post-processing may need to beperformed to clean the raw data. The sensors may be mounted to theballoon itself, and not to anything susceptible to oscillations internalto the payload support 700 and related systems. For semi-autonomousnavigation of the LTA system 100 (e.g. not relying on transmitted dataafter launch), data store can be pre-populated with the most recentavailable radiosonde data.

3. Periodically, medium period zones (Green, Yellow, Blue, High, andLow) may be recalculated, based on newly gathered and binned data. Thecalculations are fairly simple, so should not impose too much processingload.

4. Station-keeping mission layer may proceed as follows:

-   -   a. Initial height set to zonal floor, with no directional goal.    -   b. Periodically query data store for wind availability. In North        America, where/when station-keeping is possible, there will        almost always be one rare wind (north or south). This is the        priority wind. It will narrow the bounding box such that the        system attempt to keep asymmetrically further in the direction        in which the rare wind blows out of:    -   c. Once target height is initially reached, if system is within        horizontal bounds, preferentially drift upwards (during solar        heating) or downwards (at night) towards calmest winds.    -   d. If the system encounters a boundary on an axis, set main goal        to the horizontal direction opposite that boundary. Prefer        travel in the same vertical direction as the above case.    -   e. Alter the request to the direction subsystem when direction        goal changes. Direction goal is thus one of the four cardinal        directions.    -   f. Do not alter goal direction, until either reaching the        opposite boundary, or, if out of bounds on both axes, switch        priorities periodically (subject to hysteresis) to the direction        furthest out of bounds.

Below that is the direction layer which has long period parameters. Itmust translate high-level direction goals into desired heights. Itutilizes hard data to the extent it can, and shifts to heuristic data,where the hard data has expired, or where it is not available. A verysimple heuristic is used to guide the balloon to the resulting altitudearea, whereupon fine-tuning can be done by direct measurement. Oneexample of the procedure is as described as follows:

1. Zonal Ceiling: Above this height, the zonal winds cross over a secondtime, and do not seem to change any further up, all the way to ouraltitude ceiling. The exact ceiling (and other floors/ceilings) can beupdated in flight. May be set to 0, if unknown, in which case it is notconsidered.

2. Zonal Floor: Similar to Zonal Ceiling, below the zonal floor, zonalwinds do not change significantly, all the way down to aviationrestriction altitude (currently considered 45 k feet, or 13.7 km)

3. Zonal Wind Directions: specified as a simple set of positive ornegative values indicating sign of zonal wind below the zonal floor,between the zonal floor and ceiling, and above the ceiling.

4. Meridional Floor: This is a “decision” altitude. If, on a downwardexcursion, the balloon has not encountered a strong (e.g., >5 m/s)meridional wind in the desired direction (i.e. not neutral, and not theopposite direction) then there's no point in traveling any further downin the pursuit of better meridional winds. The craft will have to makedo with whatever north/south wind components are available above.

5. Wind Priority (optional): This can be automatically determined inflight, but is something that could be known prior to flight. East/Westcontrol is reliably present, or reliably absent. North or South may beavailable as well, depending on the conditions in the lower range. Thisleaves one direction always out, and often two. If only one winddirection is missing, it is considered the priority wind, and the systemneeds to spend as much time as possible in those winds, when it findsthem, because they may be absent later. See description and figureabove.

An objective of the algorithm may be described as follows:

1. Zonal control is cheap, where and when available. Meridional isgenerally fleeting.

2. Where a zonal crossover is available, green zones (ideally) or yellowzones (see zone section) as close as possible to the crossover, are theideal place to hunt for zonal corrections, particularly if acorresponding green/yellow zone exists on the opposite side of thecrossover, to toggle back and forth (avoiding excessive zonaldeflection). This is because they are known to not have strong diagonalcomponents, preventing deviation on the unintended axis.

3. By the same token, when primarily interested in large meridionalcorrections, blue zones of the appropriate sign are welcome. But bluezones are typically only on one side of the axis, so they are frequentlyof limited station-keeping use.

4. Generally, slower winds are always better for station-keeping, evenif they aren't perfect, as they can be ridden for longer beforerequiring corrections.

The direction system attempts to maintain mission layer's direction, atthe lowest possible speed. One embodiment is described here:

1. East/West goal: proceed to nearest green zone in the currentdirection of vertical travel. Failing that, the yellow zone with zonalwinds of the appropriate direction. Failing that, the zonal boundary,stopping when the desired wind is reached in all cases. If not possiblein the desired direction of travel, search in the opposite direction forall of the above. If for some reason it doesn't succeed, just go to theslowest wind region, wait some period of time, and try again.

2. North/South goal: If a North/South wind has been observed atmeridional floor, and it matches what's needed, proceed directly to it.If it hasn't been observed for 72 hours, also proceed directly to it toobserve it. Otherwise, the algorithm is the same as the East/West goal,except substituting “blue” for “yellow”. Most likely, no good zones willbe available, and the system will have to make do with what it finds, inthe calmest possible regions of the wind column.

The height system translates the height request into an action for theballast system of the compressor assembly 800 and the SPB 300(add/remove/hold). It calculates the amount of air needed in the SPB 300to balance out at the desired geopotential altitude, and runs thecompressor 810 (or vents air ballast) until this is accomplished. Whenthe predicted altitude is reached, additional fine-tuning may beperformed, to fine-tune the direction. Wind navigation may takeprecedence over the mission-specified ideal altitude, in order to makethe problem more tractable.

In some embodiments, various mission objectives require the LTA system100 to maintain a presence within a particular segment or segments ofthe upper atmosphere. For example, the segment may be determined basedon communications, line of sight, reconnaissance, or other requirements.Thus, the LTA system 100 may be required to maintain a presence in agiven segment to achieve these or other objectives. The particularsegment or segments may be bounded by one or more latitude and longitudecoordinates, radii, and/or various altitudes. In some embodiments, theLTA system maintains a presence within such segments by use of the“barber pole” technique described above. The LTA system 100 may thuspersist within the envelope shown in FIG. 12A using the various featuresdescribed herein and travelling along the cyclical path described above.For instance, the valve 870 and compressor 810 may be controlled toachieve descent and ascent of the LTA system 100 at precise locations ofthe upper atmosphere to stay within the envelope of FIG. 12A for aprolonged period of time. In some embodiments, the LTA system 100 maycyclically travel along the same or approximately the same closed pathshown in FIG. 12A. In some embodiments, the LTA system 100 may notcyclically repeat the path shown in FIG. 12A but still maintain asufficient envelope. For example, a range of altitudes and latitude andlongitude coordinates may be determined that will allow the LTA system100 to achieve a mission objective. The LTA system 100 may then travellaterally in the upper troposphere and stratosphere along differentpaths for similar segments (paths X₁ or X₂) of the barber-pole cycle.Similarly, the LTA system 100 may ascend or descend through thetropopause along different paths for similar segments (paths Y₁ or Y₂)of the barber pole cycle.

The barber pole approach may be more efficient than merely ascending anddescending continuously at the same or similar latitude and longitude.For instance, as mentioned, a mission objective may still be achieveddespite a larger envelope in the lateral direction, which may be causedby the lateral travel of the barber pole approach, for example lateraltravel along the paths X₁ and X₂. This in effect allows the ascent anddecent systems to rest and not use power during the lateral segments.Thus, the LTA system 100 may maintain a sufficient envelope but withless expenditure of power for releasing or taking in air compared toother approaches. Further, identification of slow moving layers, forexample by using the wind scoring techniques, may further allow forgreater power savings due to slower movement in the lateral direction.Identification of slower wind layers within the tropopause may also beused for power savings, where ascent and descent rates can be slower,creating larger diameter helical paths but which are still within thedesired envelope.

FIG. 12B is a flow chart showing an embodiment of a method 1200 forstation-keeping with the LTA system 100. The method 1200 may beperformed for example to achieve the persistence envelope described withrespect to FIG. 12A. The method 1200 may be performed with the variousLTA systems described herein, including the LTA systems 100 and 101, andother variations of those LTA systems.

As shown in FIG. 12B, the method 1200 begins with step 1210 wherein afirst range of latitude and longitude coordinates are determined. Step1210 may include determining a first range of latitude and longitudecoordinates corresponding to a first portion of the tropopause having afirst plurality of altitudes corresponding respectively to a firstplurality of wind directions within the tropopause. Step 1210 may beperformed by the control system 1000. In some embodiments, step 1210 isperformed by onboard computers and/or sensors, such as the sensors 1010and/or the supporting subsystems 1070. In some embodiments, step 1210 isperformed by ground stations or other LTA systems and the coordinatesare communicated to the LTA system 100. Step 1210 may involveidentifying a range that includes the point K of FIG. 12A. In someembodiments, step 1210 may include moving the LTA system 100 within thefirst range of latitude and longitude coordinates. In some embodiments,step 1210 includes the LTA system 100 travelling in a generallyhorizontal first direction through the troposphere to one of thecoordinates of the determined first range of latitude and longitudecoordinates.

The method 1200 then moves to step 1220 wherein air is released with avalve from the SPB 300 from within the first range of latitude andlongitude coordinates. Step 1220 may include release air from the SPB300 with the valve 870 while the LTA system 100 is within the firstrange of latitude and longitude coordinates. Step 1220 may be performedin the upper troposphere or in the tropopause. In some embodiments, step1220 includes controllably releasing, with the adjustable valve 870, theambient air from the SPB 300 to ascend the LTA system 100 from thedetermined first range of latitude and longitude coordinates within thetroposphere and through the tropopause to the stratosphere, wherein theLTA system 100 travels along a first helical trajectory through thetropopause due to the first plurality of wind directions at the firstplurality of altitudes within the tropopause, wherein the LTA system 100ascends at a plurality of ascent rates through the tropopause, andwherein at least one of the plurality of ascent rates is at least 10,000feet per hour.

The method 1200 then moves to step 1230 wherein the LTA system ascendsalong an upward helical trajectory. Step 1230 includes the LTA system100 ascending due to the release of air and the resulting lower mass ofair ballast in the SPB 300. Step 1230 may include the LTA system 100ascending along a helical trajectory through the tropopause. Forexample, in step 1230 the LTA system 100 may ascend along the path Y₁and/or to the point L of FIG. 12A. Step 1230 may include the LTA system100 ascending to the stratosphere.

The method 1200 then moves to step 1240 wherein a second range oflatitude and longitude coordinates are determined. Step 1240 may includedetermining a second range of latitude and longitude coordinatescorresponding to a second portion of the tropopause having a secondplurality of altitudes corresponding respectively to a second pluralityof wind directions within the tropopause. In step 1240 at least one ofthe coordinates of the first range of latitude and longitude coordinatesmay not be within the second range of latitude and longitudecoordinates. Step 1240 may be performed by the control system 1000. Insome embodiments, step 1240 is performed by onboard computers and/orsensors, such as the sensors 1010 and/or the supporting subsystems 1070.In some embodiments, step 1240 is performed by ground stations or otherLTA systems and the coordinates are communicated to the LTA system 100.Step 1240 may involve identifying a range that includes the point M ofFIG. 12A. In some embodiments, step 1240 may include moving the LTAsystem 100 within the second range of latitude and longitudecoordinates. In some embodiments, step 1240 includes the LTA system 100travelling in a generally horizontal second direction through thestratosphere to one of the coordinates of the determined second range oflatitude and longitude coordinates. In some embodiments of step 1240,the second direction travelled is different from the first directionthat may be travelled in step 1210.

The method 1200 then moves to step 1250 wherein air is pumped into theSPB 300 with a compressor 810 from within the second range of latitudeand longitude coordinates. Step 1250 may include pumping air into theSPB 300 with the compressor 810 while the LTA system 100 is within thesecond range of latitude and longitude coordinates. Step 1250 may beperformed in the upper troposphere or in the tropopause. In someembodiments, step 1250 includes controllably pumping, with thecompressor 810, the ambient air into the SPB 300 to descend the LTAsystem 100 from the determined second range of latitude and longitudecoordinates within the stratosphere and through the tropopause to thetroposphere, wherein the LTA system 100 travels along a second helicaltrajectory through the tropopause due to the second plurality of winddirections at the second plurality of altitudes within the tropopause,and wherein the LTA system 100 descends at a plurality of descent ratesthrough the tropopause, and wherein at least one of the plurality ofdescent rates is at least 10,000 feet per hour.

The method 1200 then moves to step 1260 wherein the LTA system descendsalong a downward helical trajectory. Step 1260 includes the LTA system100 descending due to the pumping in of air and the resulting highermass of air ballast in the SPB 300. Step 1260 may include the LTA system100 descending along a helical trajectory through the tropopause. Forexample, in step 1260 the LTA system 100 may descend along the path Y₂and/or to the point J of FIG. 12A. Step 1260 may include the LTA system100 descending to the upper troposphere.

The method 1200 may be cyclically repeated in various manners. Forexample, multiple LTA systems 100 may be launched and flown as describedin the method 1200. As further example, steps 1210 through 1260 may berepeated for maintaining the LTA system 100 within a persistenceenvelope, such as the envelope of FIG. 12A. In some embodiments, themethod 1200 is cyclically repeated for maintaining the LTA system 100within a persistence envelope comprising portions of the troposphere,tropopause and stratosphere, where maintaining the balloon system withinthe persistence envelope comprises cyclically repeating the following:i) the LTA system 100 travelling, from a starting position within thetroposphere corresponding to one of the coordinates of the second rangeof latitude and longitude coordinates, along the generally horizontalfirst direction through the troposphere to a first location of thetroposphere corresponding to one of the coordinates of the first rangeof latitude and longitude coordinates; ii) the LTA system 100 ascendingfrom the first location of the troposphere through the tropopause alongthe first helical trajectory to a second location within thestratosphere; ii) the LTA system 100 travelling along the generallyhorizontal second direction from the second location of the stratosphereto a third location of the stratosphere corresponding to one of thecoordinates of the second range of latitude and longitude coordinates;and iv) the LTA system 100 descending from the third location of thestratosphere through the tropopause along the second helical trajectoryto an ending position within the troposphere corresponding to one of thecoordinates of the second range of latitude and longitude coordinates.

M. Performance Simulations

The simulated performances of various embodiments of the LTA system 100for various mission requirements were analyzed. For comparison, the samesimulated performances of a “ballonet” balloon system were alsoanalyzed. The “ballonet” system uses a super pressure balloon envelopefor lift. The inside of the super pressure lifting balloon includes asecond fully sealed balloon envelope, or ballonet. The ballonet ispressurized for descent and air is released form the ballonet fordescent. The performance of the LTA system 100 in comparison to theballonet system for three missions is described in this section.

1. 60,000-80,000 Feet

The first mission or simulation is a nominal altitude control range of20,000 ft, operating between 60,000 ft and 80,000 ft. This range andaltitude combination allows for access to a large variety of winddirections and speeds throughout much of the year. This type of variablewind access could allow for either a large degree of trajectory controlor the possibility of station keeping over certain areas of the globefor as long as days, weeks, and in some cases even months.

To allow for initial system sizing a payload mass of 128.4 kg wasassumed. This payload mass was determined by first sizing the LTA system100 with a total ZPB 200 suspended weight capability of 250 kg. The SPB300 envelope was sized with a maximum change in pressure (ΔP) capabilityof 3500 Pa at a volume of 1200 m³. The mass of this ballast envelope wasdetermined to be 121.6 kg leaving the remaining 128.4 kg for thepayload. This payload mass is assumed to include the mass of thecompressor/vent system, the power system, the flight avionics, and themission specific payload and instrumentation. The ballonet system doesnot require a tandem balloon so was sized to be able to lift the 128.4kg payload to the maximum float altitude with a maximum super pressurecapability of 1200 Pa. For this simulation the compressor 810 and powersubsystem was assumed to be the same for both systems in order to removeit as a variable and to force a closed design for the ballonet system.Accordingly, it was sized to deliver a maximum discharge pressure of3500 Pa at 350 liters/second at all the target altitudes. The ventarchitectures between the two systems, however, were sized differentlyto account for the large difference in the ballast balloon volumes. Forthe LTA system 100 architecture, a vent diameter of 50 mm was assumedand for the large ballonet architecture a vent diameter of 150 mm wasassumed. Table 2 summarizes the two system designs used for simulation#1.

TABLE 2 Simulation #1 altitude control system parameters of LTA system100 versus ballonet system. Parameter LTA System 100 Ballonet SystemMass of Helium at Launch 58 98 (kg) Mass of Helium Vented (kg) 5 0Volume of Lift Balloon (m3) 15052 10033 Mass of Lift Balloon (kg) 77 432Mass of Ballast Balloon (kg) 121.6 25 Payload Mass (kg) 128.4 128.4Total System Mass (kg) 327 585.4

The flight simulation for this first simulation was run for 96 hours andhad several different altitude inputs. Initially both systems were takento their maximum float altitude of 80,000 ft., and then altitude changeinputs were commanded as follows: Hour: 2, Altitude: 80,000 ft.; Hour:21, Altitude: 60,000 ft.; Hour: 30, Altitude: 80,000 ft.; Hour: 48,Altitude: 60,000 ft.; and Hour: 55, Altitude: 80,000 ft.

For the LTA system 100, only a low amount of free lift (5%) is requiredfor nominal flight operations. However 10% to 15% free lift may berequired to penetrate the cold temperatures of the troposphere andascend to the nominal float altitude. For the purposes of thissimulation the excess lift gas is being dumped passively by allowing theballoon system to ascend early in the flight when solar heating causesthe lift gas to expand the ZPB 200 envelope to its maximum designvolume. Gas that expands beyond this volume is vented from the ZPB 200by design. Because of its passive nature this is a conservative approachto venting the excess lift gas. However, in some embodiments, activelyopening a valve located near the top of the ZPB 200 may also accomplishthis task, thereby avoiding the early high altitude maneuver ifrequired. The ballonet approach also requires 10% to 15% free lift forinitial ascent, but all the lift gas is retained for nominal operation.

The performance summary for simulation #1 is shown in Table 3. Someconclusions that can be drawn from simulation #1 are that if the samecompressor characteristics are assumed for both systems, the LTA system100 architecture has more than double the descent rate of the ballonetsystem, while at the same time requiring less than half of thecumulative volume of atmospheric air to be pumped into the ballast tank,and therefore less than half of the total power usage. In addition, thesame LTA system 100 configuration can cover a total altitude range ofabout 65,000 ft., which is more than double that of the ballonet systemused in this simulation. The ballonet system, however, is more stable ata given altitude than is the LTA system 100 architecture, but alsorequires 68% more lift gas.

TABLE 3 Simulation #1 performance summary of LTA system 100 versusballonet system. Parameter LTA System 100 Ballonet System Maximum AscentRate (fph) 3300 3300 Maximum Descent Rate (fph) 5600 1700 AltitudeStability (+/− ft.) 450 50 Compressor Volume 9,200,000 19,200,000 Pumped(liters) Compressor ON time (hrs.) 7.3 15.2 Energy (kW-h) 7.3 15.2 MaxAltitude Range (Δft) 65,000 30,000

In particular, the resulting analysis of simulation #1 showed that theLTA system 100 requires active control of the SPB 300 pressure over awider range of differential pressures during operations than theballonet system. This is required to both maintain altitude during solarfluctuations when the lift balloon increases and decreases in volume aswell as to actively change altitude when commanded. Additionally, toperform the proscribed maneuvers the LTA system 100 requires a higherdifferential pressure than the ballonet system because of thesignificantly smaller size of its ballast tank. The LTA system 100requires a maximum ΔP of 3500 Pa to perform rapid descents from 80,000ft. down to 60,000 ft., however most of the operational time the systemrequires less than 3000 Pa for operation. The ballonet in contrast onlyrequires a maximum ΔP of ˜500 Pa to perform operations, however itsoperational response time is much, much slower because of the length oftime necessary to transfer the amount of air required for altitudeadjustment into or out of the ballast tank. In other words, for thedescent maneuvers in particular, even though the ballast tank holds morepressure than is used, there is not enough time to add the additionalballast before the next ascent command is given. Ascent maneuvers alsotake place much more slowly with the ballonet system than the LTA system100 because so much more ballast must be vented to enable ascent.

The resulting analysis of simulation #1 also showed that, even with thecontinuous, small SPB 300 pressure adjustments required for stablealtitude retention, the LTA system 100 requires less than half of theoverall air volume to be pumped, as compared to the ballonet system,over the duration of the mission (9.2 million vs 19.2 million liters).This was also with significantly improved ascent and descent rates forthe LTA system 100. Less total pumped volume equates to less total‘pump-on’ time of the compressor 810 and therefore less overall powerrequired.

A final metric that can be pulled from the two designs compared in thissimulation is the maximum total altitude changes the systems, asdesigned, are capable of performing. This was done by iterating themission with lower and lower target altitudes until control authoritywas eventually lost. The LTA system 100 used for Simulation 1 is capableof descending in altitude to 20,000 ft. (total altitude changecapability of ˜65,000 ft) in comparison to the ballonet system which isonly capable of descent to 50,000 ft. (total altitude change capabilityof ˜30,000 ft). Because of the ballonet ballast tank total differentialpressure limitation of 1200 Pa, the ballonet system loses controlauthority over the altitude much earlier than does the LTA system 100.

2. 85,000-95,000 Feet

The second mission or simulation was developed to look at altitudecontrol system limitations for higher altitude use than that chosen forSimulation #1. Accordingly, a nominal range of 85,000 ft. to 95,000 ft.was chosen. The primary driver for this simulation was to determine anyperformance limitations when scaling the systems to allow for higheraltitudes and larger payloads versus the performance examined at themore favorable altitudes for station keeping and trajectory control usedin the first simulation. For the sake of comparability betweensimulations the same payload mass (128.4 kg) was used to size bothsystems for this simulation as was used in simulation #1. Additionally,the same power and compressor system, capable of delivering a maximumdischarge pressure of 3500 Pa at 3501/s, was used and the ventarchitectures were sized for each system as with the simulation #1. TheZPB 200 envelope of the LTA system 100 was sized to have maximum volumeat 100,000 ft. to allow for the same high altitude excess free lift dumpmaneuver as was used early in the mission for simulation #1, however thesame simulation #1 ballast tank parameters were retained (3500 Pamaximum differential pressure at 1200 m³). The challenge for theballonet system was then to size it to be able to lift the 128.4 kgpayload to the maximum float altitude. This required a significantincrease in lift balloon size (from 10033 m³ to 43187 m³) whilesimultaneously keeping the overall mass as low as possible. This wasdone by reducing the material thickness as much as possible, howeverthis also resulted in a reduction of the maximum differential pressurecapability of the balloon from 1200 Pa to 900 Pa. Table 4 summarizes thetwo system designs used for simulation #2.

TABLE 4 Simulation #2 altitude control system parameters of LTA system100 versus ballonet system. Parameter LTA System 100 Ballonet SystemMass of Helium at Launch 70 132 (kg) Mass of Helium Vented (kg) 8 0Volume of Lift Balloon (m3) 29562 43187 Mass of Lift Balloon (kg) 138565 Mass of Ballast Balloon (kg) 121.6 65 Payload Mass (kg) 128.4 128.4Total Mass (kg) 388 758.4

The flight simulation for simulation #2 was run for 96 hours, as withsimulation #1, to compare the performance of both systems. Both systemswere initially commanded to the maximum float altitude and then werecommanded to follow a specific altitude profile as follows: Hour: 2,Altitude: 95,000 ft.; Hour: 21, Altitude: 85,000 ft.; Hour: 55,Altitude: 95,000 ft.; Hour: 72, Altitude: 85,000 ft.; Hour: 84,Altitude: 95,000 ft.

The performance summary for simulation #2 is shown in Table 5. ForSimulation #2, again with the same compressor characteristics used forboth systems, the LTA system 100 architecture demonstrated a much higherdescent rate than the ballonet system and still required less total‘pump on’ time and power usage. It must also be taken into account thatthe second altitude descent for the ballonet system was not fullycompleted in the time required, thus allowing for less ‘on time’ thanthe mission parameters nominally called for. Recall also that the designsolution for the ballonet system used for this simulation represents adesign solution that likely doesn't close because of its sheer size andcomplexity. Also, as noted in simulation #1, the stability of theballonet system is greater than that of the LTA system 100 system, whichis seen to become more unstable than observed at the lower altitudesimulation. Further, note that an extensibility comparison to examinethe maximum altitude change each system could achieve was not performedfor this simulation, but is addressed in simulation #3 which uses thesame general systems designs. This simulation #2 clearly demonstratesthat the ballonet system cannot adequately control altitude at highoperating altitudes. Attempts to increase the descent rate for theballonet system causes the design solution to diverge—the super pressureballoon size of the ballonet system and structural requirements growwith the larger compressor and power system mass, leading to a largersuper pressure balloon in the next iteration, and so on with increasingdivergence in each iteration.

TABLE 5 Simulation #2 performance summary of LTA system 100 versusballonet system. Parameter LTA System 100 Ballonet System Maximum AscentRate (fph) 5700 5600 Maximum Descent Rate (fph) 10000 600 AltitudeStability (+/− ft.) 150 50 Compressor Volume Pumped 32,600,00034,500,000 (liters) Compressor ON time (hrs.) 25.9 27.4 Energy (kW-h)25.9 27.4 Max Altitude Range (Δft) 75,000 17,500

In particular, the ballonet system is more stable at a given altitudethan is the LTA system 100, however the ballonet system also requiresmuch, much more time to respond to altitude adjustments. In particular,the maximum descent rate for the ballonet system was only about 600ft./hr., whereas the maximum descent rate for the LTA system 100 wasclose to 10,000 ft./hr., or about 16.5 times faster. Further, the LTAsystem 100 once again utilized its maximum ΔP of 3500 Pa, however theballonet system was only able to use 400 Pa of the 900 Pa limit becauseof the massive volume of the ballast tank in comparison to the volumeflow rate of the compressor 810. Also, the LTA system 100 requires fewertotal liters pumped (32,600,000 liters versus 34,500,000 liters),although at less of a difference than in simulation #1, but withsignificantly improved ascent and descent rates.

3. 85,000-95,000 Feet with Normalized Compressor

For simulations #1 and #2 above, a common compressor and power systemwas utilized in order to remove these as variables for the sake ofcomparison. However, the flow rate limitation of 350 liters/secondlimited the ascent and decent rate achievable by the ballonet system.Therefore, for simulation #3, the ballonet system from simulation #2 wasaltered to include a hypothetical 3,500 liter per second (lps)compressor (ignoring the volume, mass, and power requirements such a 10×system might have) in order to compare the LTA system 100 and ballonetsystem with more normalized or even performance characteristics. Theoriginal compressor assumptions were retained for the LTA system 100.Thus, the only change made between simulations #2 and #3 were to theassumed pump performance capabilities, and system parameters are thesame as shown in Table 5.

The results showed that the 10× enhanced compressor system used for theballonet system produced ascent and descent rates much closer to the LTAsystem 100 performance characteristics than simulations #1 and #2.However, as mentioned, the 10× compressor capability of the ballonet isunrealistic for practical implementation and is used for analysis only.With this enhancement came a substantially reduced ‘pump on’ time forthe ballonet system, however it had to move ten times the air in thattime period which still required more power than the same LTA system 100architecture as simulations #1, #2 and #3. Further, once again the LTAsystem 100 was able to demonstrate a substantially larger overallaltitude range than the equivalent ballonet system. However, theballonet system was again superior in its ability to hold a stablealtitude because of its constant overall volume.

In particular, for simulation #3 several conclusions can be drawn withregards to the use of the theoretical 3,500 lps pump system as part ofthe ballonet architecture. First, it performs extremely smoothly withaltitude ascents and descents that rival the LTA system 100 architecturewhile maintaining altitude consistently through diurnal cycling, as wasthe intent of this exercise. Second, the ballast tank pressure onlyincreases to 460 Pa. However, while the system performance is enhanced,it also requires more cumulative compressor air volume pumped over thecourse of the operational simulation than does the equivalent LTA system100 system, which equates to more power required. This is true despitethe fact that the actual “on” time for the ballonet pump is considerablyless (3.1 hrs) than for the LTA system 100 architecture (25.9 hrs).

Further, the same extensibility exercise was performed with simulation#3 as was undertaken for simulation #1. For each system the altitude wasiteratively decreased from the maximum float altitude until controlauthority was lost over the balloon and it was no longer able tofunction at the commanded altitude. The results showed that the LTAsystem 100 is capable of descending in altitude to 20,000 ft. for anoverall maximum altitude change capability of about 75,000 ft. Theballonet system, in comparison, is only capable of descent to 77,500feet, or a total altitude change of 17,500 ft. Below this altitude theballonet system lift balloon begins to hit its maximum pressurecapability and, in the simulation, lift gas is vented to prevent theballoon from bursting. With these observations it can be concluded thateven with an unrealistically enhanced compressor and power system thatwould allow it to match the performance characteristics of the LTAsystem 100 architecture at altitudes between 85,000 ft. and 95,000 ft.,the ballonet system can really only function reliably at or near themission specific altitudes that allow for taking full advantage ofvariable winds for steering.

4. Summary of Simulations #1, #2 and #3

Simulation #2 provides the clearest demonstration of the system levelimpact of controlling altitude at higher altitudes. As operatingaltitude requirements are elevated into the 29 km (95,000 ft.) altituderange, it becomes more difficult (energetically and mechanically) tochange altitude with a ballonet system because air densitylogarithmically decreases with altitude. This requires the ballonetcompressor to pump larger volumes of lower density air in order tocompress the lift gas as well as the ballast air into the one largesuper pressure balloon with an air ballonet. Sufficiently pressurizingthe large ballonet balloon to get useful descent rates of about 2 km/h(109 feet per minute) also imparts hoop-stress structural loads on thelarge super pressure ballonet balloon that significantly exceed currentdesigns and materials. Furthermore, once the ballonet system reaches thetarget operating altitude, it is trapped with no real ability todescend. Using the same compressor and power system, the LTA system 100has an average descent rate of 3.05 km/h (167 feet per minute) whereasthe ballonet system can only achieve 0.18 km/h (10 feet per minute).

Further, the use of a ballonet system for these missions is unrealisticas the design of a useful ballonet system operating at 29 km (95,000ft.) does not close. Achieving a useful descent rate requires acompressor capable of 10× the flow rate used in the example above. Sucha large compressor and power system for the ballonet system causes thesuper pressure balloon volume to grow dramatically at the high altitude,which drives up the compressor and power system mass as well as thehoop-stress in the super pressure balloon, further causing the design todiverge. By only actively compressing ballast air in a small separateballoon, as in the SPB 300 of the LTA system 100, the compressor 810 andpower system mass readily closes for the LTA system 100 altitude controlsystem.

Based on the comparative simulations performed in this study the LTAsystem 100 altitude control system is superior in three importantmetrics used to rate the performance of the two systems: Ascent/DescentRate, Altitude Range and Power Consumption. However, because of itsconstant volume architecture, the ballonet system has the advantage inaltitude stability.

In particular, the ascent/descent advantage goes to the LTA system 100architecture because it is a lower mass system and therefore requires acomparatively smaller ballast tank, i.e. the SPB 300, than the ballonetsystem. With existing, state of the art compressor technology the SPB300 of the LTA system 100 can simply be pressurized at a faster rate. Assimulation #3 demonstrated, even with the ballonet system having acompressor flow rate at ten times that of the LTA system 100 compressor810, the ascent and descent rates of the ballonet system were still lessthan the LTA system 100 architecture.

The altitude range advantage also goes to the LTA system 100architecture because it has a lower overall system mass and is thereforemore greatly affected by the ballast in the SPB 300. The SPB 300 volumeis also not structurally tied to the ZPB 200 lifting balloon and cantherefore be designed to any volume necessary to accomplish missionparameters. On the other hand, because it is so structurally tied to themechanical properties of its super pressure lift balloon, the ballonetsystem can only accept so much volume increase before it challenges thestructural integrity of the lift balloon envelope. The ballonet systemarchitecture does not close for useful altitude control rates operatingnear the 29 km (95,000 ft.) altitude range.

Further, because the SPB 300 of the LTA system 100 can pressurize anddepressurize much more quickly than the ballonet ballast tank, the LTAsystem 100 architecture also has the advantage in terms of overall powerusage for the same mission parameters at lower altitudes.

However, the results also showed that the LTA system 100 architecturedoes fall short of the ballonet system performance in terms of altitudestability. Because the ZPB 200 required for the LTA system 100architecture changes volume in response to the ever changing solarheating cycle, the pressure of the SPB 300 must be continually adjustedin order to hold altitude. In contrast, the ballonet system for liftuses a super pressure balloon, which is not subjected to volume changedue to solar heating and cooling. Even with the constant, smallcompressor inputs required by the LTA system 100 for altitude stability,however, it has been shown that the LTA system 100 architecture requiresless power than the ballonet approach. However, due to the wind analysesperformed it was determined that the stability of the LTA system 100system met the requirements of the system to remain within a particularwind layer.

The flow chart sequences are illustrative only. A person of skill in theart will understand that the steps, decisions, and processes embodied inthe flowcharts described herein may be performed in an order other thanthat described herein. Thus, the particular flowcharts and descriptionsare not intended to limit the associated processes to being performed inthe specific order described.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers. The scope of the invention is indicated by the appended claimsrather than by the foregoing description. All changes which come withinthe meaning and range of equivalency of the claims are to be embracedwithin their scope.

The foregoing description details certain embodiments of the systems,devices, and methods disclosed herein. It will be appreciated, however,that no matter how detailed the foregoing appears in text, the systems,devices, and methods may be practiced in many ways. As is also statedabove, it should be noted that the use of particular terminology whendescribing certain features or aspects of the invention should not betaken to imply that the terminology is being re-defined herein to berestricted to including any specific characteristics of the features oraspects of the technology with which that terminology is associated.

It will be appreciated by those skilled in the art that variousmodifications and changes may be made without departing from the scopeof the described technology. Such modifications and changes are intendedto fall within the scope of the embodiments. It will also be appreciatedby those of skill in the art that parts included in one embodiment areinterchangeable with other embodiments; one or more parts from adepicted embodiment may be included with other depicted embodiments inany combination. For example, any of the various components describedherein and/or depicted in the Figures may be combined, interchanged orexcluded from other embodiments.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art may translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that virtually any disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms. For example, the phrase “A or B” will be understood toinclude the possibilities of “A” or “B” or “A and B.”

All references cited herein are incorporated herein by reference intheir entirety. To the extent publications and patents or patentapplications incorporated by reference contradict the disclosurecontained in the specification, the specification is intended tosupersede and/or take precedence over any such contradictory material.

The term “comprising” as used herein is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps.

All numbers expressing quantities of ingredients, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.” Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe specification and attached claims are approximations that may varydepending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should be construed in light of the number ofsignificant digits and ordinary rounding approaches. For example, termssuch as about, approximately, substantially, and the like may representa percentage relative deviation, in various embodiments, of ±1%, ±5%,±10%, or ±20%.

The above description discloses several methods and materials of thepresent invention. This invention is susceptible to modifications in themethods and materials, as well as alterations in the fabrication methodsand equipment. Such modifications will become apparent to those skilledin the art from a consideration of this disclosure or practice of theinvention disclosed herein. Consequently, it is not intended that thisinvention be limited to the specific embodiments disclosed herein, butthat it cover all modifications and alternatives coming within the truescope and spirit of the invention as embodied in the attached claims.

What is claimed is:
 1. A lighter-than-air (LTA) high altitude balloonsystem comprising: a zero-pressure balloon (ZPB) configured to receivetherein an LTA gas to provide an upward lifting force to the balloonsystem; a super-pressure balloon (SPB) having an outer skin andconfigured to couple with the ZPB, the outer skin defining an interiorvolume configured to receive therein a variable amount of ambient airfrom a surrounding atmosphere to provide a variable downward force tothe balloon system, the SPB external to and suspended from the ZPB; acentrifugal compressor in fluid communication with the ambient air andwith the interior volume of the SPB, the centrifugal compressorconfigured to compress the ambient air and pump the compressed ambientair into the interior volume of the SPB to increase the downward forceto the balloon system; an adjustable valve in fluid communication withthe ambient air and with the interior volume of the SPB, the valveconfigured to be adjusted to release the compressed ambient air from theinterior volume of the SPB to the surrounding atmosphere to decrease thedownward force to the balloon system; a sensor coupled with the balloonsystem and configured to detect an environmental attribute; a controlsystem in communicating connection with the sensor, with the centrifugalcompressor, and with the adjustable valve, the control system configuredto control the centrifugal compressor and the adjustable valve based atleast on the detected environmental attribute to control the amount ofcompressed air inside the SPB to control an altitude of the balloonsystem; a plurality of tendons coupled with the SPB and extending alongan exterior of the outer skin of the SPB, the plurality of tendonsconfigured to bias the SPB into a substantially pumpkin shape at leastwhen a first pressure inside the SPB is greater than a second pressureof the surrounding atmosphere; a payload support coupled with the SPBand configured to support a payload; an elongated ladder assemblycoupling the payload support with the SPB such that the payload supportis located above or below the SPB when the balloon system is in flight;a solar array coupled with the elongated ladder assembly; and an airhose fluidly coupled with the centrifugal compressor, wherein thecentrifugal compressor is fluidly coupled with the interior volume ofthe SPB via the air hose.
 2. The high altitude balloon system of claim1, wherein the centrifugal compressor comprises two or more stages. 3.The high altitude balloon system of claim 1, wherein the centrifugalcompressor is configured to provide at least 500 liters of the ambientair per second to the interior volume of the SPB at altitudes above50,000 feet.
 4. The high altitude balloon system of claim 1, wherein thecentrifugal compressor is configured to provide the ambient air to theinterior volume of the SPB such that a resulting descent rate of theballoon system is at least 10,000 feet per hour at altitudes above50,000 feet.
 5. The high altitude balloon system of claim 1, wherein theadjustable valve is configured to be adjusted to release the pumped-inambient air from the interior volume of the SPB to the surroundingatmosphere such that a resulting ascent rate of the balloon system is atleast 10,000 feet per hour at altitudes above 50,000 feet.
 6. The highaltitude balloon system of claim 1, wherein the centrifugal compressorcomprises two or more stages, and is configured to provide at least 500liters of the ambient air per second to the interior volume of the SPBsuch that a resulting descent rate of the balloon system is at least10,000 feet per hour at altitudes above 50,000 feet, and wherein theadjustable valve is configured to be adjusted to release the pumped-inambient air from the interior volume of the SPB to the surroundingatmosphere such that a resulting ascent rate of the balloon system is atleast 10,000 feet per hour at altitudes above 50,000 feet.
 7. The highaltitude balloon system of claim 1, wherein the balloon system comprisestwo or more SPBs connected in series.
 8. The high altitude balloonsystem of claim 1, wherein the air hose extends along and is supportedat least in part by the elongated ladder assembly, and the centrifugalcompressor is mounted with the payload support.
 9. The high altitudeballoon system of claim 1, further comprising a parafoil system coupledwith the payload support and releasably coupled with the elongatedladder assembly in a stowed configuration, the parafoil systemconfigured to release from the elongated ladder assembly and to deployinto a deployed flight configuration to controllably descend with thepayload support to a landing site.
 10. The high altitude balloon systemof claim 9, wherein the solar array includes one or more solar panelscoupled with the elongated ladder assembly.
 11. The high altitudeballoon system of claim 1, further comprising a gimbal rotatablycoupling the ZPB with the SPB, the gimbal configured to rotate the SPBrelative to the ZPB, wherein the SPB and the solar array are rigidlycoupled with the elongated ladder assembly such that rotation of the SPBwith the gimbal rotates the elongated ladder assembly and the solararray to a desired orientation.
 12. The high altitude balloon system ofclaim 11, wherein the ZPB comprises one or more gores, and the gimbalcomprises upper and lower separable portions, the balloon system furthercomprising: one or more release lines coupling the upper and lowerseparable portions of the gimbal, the one or more release linesextending adjacent a hot wire configured to be heated and thereby burnthe one or more release lines, wherein burning the one or more releaselines separates the upper and lower separable portions of the gimbal;and a tear line coupled with the ZPB and with the lower portion of thegimbal, the tear line configured to at least partially remove the one ormore gores of the ZPB due to separation and falling away of the lowerportion of the gimbal from the ZPB.
 13. The high altitude balloon systemof claim 12, wherein the payload support comprises a tetrahedral framecoupled with the SPB.
 14. The high altitude balloon system of claim 1,wherein the payload support has a tetrahedral frame.
 15. A method ofcontrolling a lighter-than-air (LTA) high altitude balloon systemthrough a troposphere, tropopause and stratosphere, the balloon systemcomprising a zero-pressure balloon (ZPB) coupled with a super-pressureballoon (SPB), the SPB external to and suspended from the ZPB, acentrifugal compressor fluidly coupled with the SPB and configured topump ambient air into the SPB, an adjustable valve fluidly coupled withthe SPB and configured to release the pumped-in ambient air from theSPB, a payload support coupled with the SPB and configured to support apayload, an elongated ladder assembly coupling the payload support withthe SPB such that the payload support is located above or below the SPBwhen the balloon system is in flight, a solar array coupled with theelongated ladder assembly, and an air hose fluidly coupled with thecentrifugal compressor, wherein the centrifugal compressor is fluidlycoupled with an interior volume of the SPB via the air hose, the methodcomprising: determining a first range of latitude and longitudecoordinates corresponding to a first portion of the tropopause having afirst plurality of altitudes corresponding respectively to a firstplurality of wind directions within the tropopause; controllablyreleasing, with the adjustable valve, the ambient air from the SPB toascend the balloon system from the determined first range of latitudeand longitude coordinates within the troposphere and through thetropopause to the stratosphere, wherein the balloon system travels alonga first helical trajectory through the tropopause due to the firstplurality of wind directions at the first plurality of altitudes withinthe tropopause, wherein the balloon system ascends at a plurality ofascent rates through the tropopause, and wherein at least one of theplurality of ascent rates is at least 10,000 feet per hour; determininga second range of latitude and longitude coordinates corresponding to asecond portion of the tropopause having a second plurality of altitudescorresponding respectively to a second plurality of wind directionswithin the tropopause; and controllably pumping, with the compressor,the ambient air into the SPB to descend the balloon system from thedetermined second range of latitude and longitude coordinates within thestratosphere and through the tropopause to the troposphere, wherein theballoon system travels along a second helical trajectory through thetropopause due to the second plurality of wind directions at the secondplurality of altitudes within the tropopause, and wherein the balloonsystem descends at a plurality of descent rates through the tropopause,and wherein at least one of the plurality of descent rates is at least10,000 feet per hour.
 16. The method of claim 15, wherein at least oneof the coordinates of the first range of latitude and longitudecoordinates is not within the second range of latitude and longitudecoordinates.
 17. The method of claim 15, further comprising: travellingin a generally horizontal first direction through the troposphere to oneof the coordinates of the determined first range of latitude andlongitude coordinates before controllably releasing the ambient air toascend the balloon system through the tropopause and into thestratosphere; and travelling in a generally horizontal second directionthrough the stratosphere to one of the coordinates of the determinedsecond range of latitude and longitude coordinates after ascending tothe stratosphere and before controllably pumping in the ambient air todescend the balloon system through the tropopause and into thetroposphere, wherein the first direction is different from the seconddirection.
 18. The method of claim 17, further comprising: maintainingthe balloon system within a persistence envelope comprising portions ofthe troposphere, tropopause and stratosphere, wherein maintaining theballoon system within the persistence envelope comprises cyclicallyrepeating the following: travelling, from a starting position within thetroposphere corresponding to one of the coordinates of the second rangeof latitude and longitude coordinates, along the generally horizontalfirst direction through the troposphere to a first location of thetroposphere corresponding to one of the coordinates of the first rangeof latitude and longitude coordinates; ascending from the first locationof the troposphere through the tropopause along the first helicaltrajectory to a second location within the stratosphere; travellingalong the generally horizontal second direction from the second locationof the stratosphere to a third location of the stratospherecorresponding to one of the coordinates of the second range of latitudeand longitude coordinates; and descending from the third location of thestratosphere through the tropopause along the second helical trajectoryto an ending position within the troposphere corresponding to one of thecoordinates of the second range of latitude and longitude coordinates.19. A lighter-than-air (LTA) high altitude balloon system comprising: azero-pressure balloon (ZPB) configured to receive therein an LTA gas toprovide an upward lifting force to the balloon system; a super-pressureballoon (SPB) configured to couple with the ZPB and configured toreceive ambient air within an interior volume to provide a downwardforce to the balloon system, the SPB external to and suspended from theZPB; and a multi-stage centrifugal compressor configured to pump theambient air into the SPB to increase the downward force to the balloonsystem, wherein the multi-stage centrifugal compressor is configured topump the ambient air into the SPB such that a resulting descent rate ofthe balloon system is at least 10,000 feet per hour at altitudes above50,000 feet; an adjustable valve configured to release the pumped-inambient air from the SPB to decrease the downward force to the balloonsystem, wherein the adjustable valve is configured to release thepumped-in ambient air from the SPB such that a resulting ascent rate ofthe balloon system is at least 10,000 feet per hour at altitudes above50,000 feet; a payload support coupled with the SPB and configured tosupport a payload; an elongated ladder assembly coupling the payloadsupport with the SPB such that the payload support is located above orbelow the SPB when the balloon system is in flight; a parafoil systemcoupled with the payload support and releasably coupled with theelongated ladder assembly in a stowed configuration, the parafoil systemconfigured to release from the elongated ladder assembly and to deployinto a deployed flight configuration to controllably descend with thepayload support to a landing site; and an air hose fluidly coupled withthe multi-stage centrifugal compressor, wherein the multi-stagecentrifugal compressor is fluidly coupled with the interior volume ofthe SPB via the air hose.
 20. The system of claim 19, wherein the SPB issubstantially pumpkin-shaped at least when a first pressure inside theSPB is greater than a second pressure of a surrounding atmosphere.